P0400-P0499
P0400-P0499

P0400-P0499 – Auxiliary Emissions Controls. OBD-II

  • P0400 Exhaust Gas Recirculation Flow Malfunction
  • P0401 Exhaust Gas Recirculation Flow Insufficient Detected

What Does OBD-II Fault Code P0401 Mean?

OBD-II Code P0401 is defined as a Insufficient EGR Flow

P0401 Symptoms

  • Check Engine Light will illuminate
  • In most cases, there are no adverse conditions noticed by the driver
  • In some cases, there may be performance problems, such as pinging on acceleration, when the engine is under load or when driving the vehicle at higher speeds

Common Problems That Trigger the P0401 Code

  • Restriction in the EGR passages, usually caused by carbon buildup
  • The EGR Valve is defective
  • Lack of proper vacuum or electrical signal to the EGR valve
  • Malfunctioning EGR Vacuum supply solenoid
  • Lack of proper EGR system feedback to the computer from the:
    • Manifold Absolute Pressure Sensor (MAP)
    • Differential EGR Pressure Feedback Sensor (DPFE)
    • EGR Valve Position Sensor (EVP)
    • EGR Temperature Sensor

The Basics

NOx gases are formed when the combustion temperature is too high (2500° F). EGR systems are used to reduce the combustion temperature, thus reducing NOx formation.

The exhaust gas recirculation (EGR) system recycles a small amount of exhaust gas from the exhaust system (usually no more than 10 percent) and mixes it with the intake manifold air entering into the combustion chambers. The addition of this inert (or non-combustible) exhaust gas limits the peak combustion temperatures to a range that is below 2500° F, where the formation of nitrogen oxide (NOx) is know to occur. In some cases where the engine is pinging and/or knocking badly from a severe lack of EGR flow, misfires can take place which allow raw hydrocarbons (HC) to be released from the tailpipe.

P0401 Diagnostic Theory for Shops and Technicians

When the computer sets a code P0401, it means that the EGR flow monitoring criteria has not been met. The EGR monitoring criteria are a set of test values and are usually run during at least two different driving conditions—steady speed freeway driving and steady speed city driving.

The engine control module determines proper EGR flow in many ways:

  • Temperature increase in the EGR passages when the EGR is supposed to be flowing
  • Measurable amount of Manifold Pressure change when the EGR is supposed to be flowing
  • Measurable change (usually a decrease) in the front Oxygen Sensor Signal
  • Position change in the EGR valve as measured by an EGR Valve Position Sensor
  • Amount of Spark Knock as measured by the Knock Sensor
  • Amount of decrease in exhaust back pressure as measured by the Digital EGR Pressure Feedback Sensor

The code P0401 is often not a problem with the EGR valve itself. Rather, the EGR system is not allowing enough EGR to flow back into the combustion process to sufficiently cool the peak firing temperatures. Once the code P401 has been retrieved with a scan tool, the freeze frame data should be documented and analyzed in order to determine what engine conditions were present when the code was triggered. It is recommended that the vehicle be driven in such a way as to duplicate the code setting conditions with a data streaming scan tool connected, so the behavior of the EGR actuating components and feedback sensors can be monitored.

Common Tests to Determine Whether the Problem Is an EGR Control Problem, a Clogged or Restricted System, or a Defective Feedback Device

  • Does the engine die, not just stumble, when the EGR valve is manually raised to its maximum?
    (Use either a vacuum pump or bi-directional scan tool if it’s a digital EGR valve.)
  • Is the EGR valve getting sufficient vacuum? (Use the manufacturer EGR vacuum spec.)
  • Is the EGR system restricted? (The engine stumbles, but does not die.)
  • Is the EGR system plugged? (Engine RPM does not change.)
  • Does the EGR valve work?
  • Raise the RPM to 3000 and check manifold vacuum. Then open the EGR valve to its maximum—the manifold vacuum should drop by at least 3″ of mercury. If it does not, there is a flow and/or restriction problem.
  • Test the EGR temperature sensor (if equipped) with a propane torch and a DVOM.
  • Test the accuracy of the EGR valve position sensor with a scan tool or DVOM by raising or lowering the EGR valve.
  • Test the Digital EGR Pressure Feedback Sensor (DPFE) with a data streaming scan tool to verify that the voltage or lift percentage changes according to spec.
  • Verify that the front Oxygen Sensor readings drop and the Short Term Fuel Trim increases when the EGR valve opens. (EGR leans out the mixture.)

Note

If the NOx goes down when the EGR valve is raised (this test is most commonly performed on a Dynamometer), it is likely that one or more EGR passages or cylinders are plugged or very restricted, making the EGR only go to one or two cylinders. When this occurs, you may notice misfires and even have misfire codes along with the P0401. This can occur on vehicles that use EGR “runners” for each cylinder.


  • P0402 Exhaust Gas Recirculation Flow Excessive Detected
  • P0403 Exhaust Gas Recirculation Circuit Malfunction
  • P0404 Exhaust Gas Recirculation Circuit Range/Performance
  • P0405 Exhaust Gas Recirculation Sensor A Circuit Low
  • P0406 Exhaust Gas Recirculation Sensor A Circuit High
  • P0407 Exhaust Gas Recirculation Sensor B Circuit Low
  • P0408 Exhaust Gas Recirculation Sensor B Circuit High
  • P0409 Exhaust Gas Recirculation Sensor “A” Circuit
  • P040A Exhaust Gas Recirculation Temperature Sensor “A” Circuit
  • P040B Exhaust Gas Recirculation Temperature Sensor “A” Circuit Range/Performance
  • P040C Exhaust Gas Recirculation Temperature Sensor “A” Circuit Low
  • P040D Exhaust Gas Recirculation Temperature Sensor “A” Circuit High
  • P040E Exhaust Gas Recirculation Temperature Sensor “A” Circuit Intermittent/Erratic
  • P040F Exhaust Gas Recirculation Temperature Sensor “A”/”B” Correlation
  • P0410 Secondary Air Injection System Malfunction
  • P0411 Secondary Air Injection System Incorrect Flow Detected
  • P0412 Secondary Air Injection System Switching Valve A Circuit Malfunction
  • P0413 Secondary Air Injection System Switching Valve A Circuit Open
  • P0414 Secondary Air Injection System Switching Valve A Circuit Shorted
  • P0415 Secondary Air Injection System Switching Valve B Circuit Malfunction
  • P0416 Secondary Air Injection System Switching Valve B Circuit Open
  • P0417 Secondary Air Injection System Switching Valve B Circuit Shorted
  • P0418 Secondary Air Injection System Relay “A” Circuit Malfunction
  • P0419 Secondary Air Injection System Relay “B” Circuit Malfunction
  • P041A Exhaust Gas Recirculation Temperature Sensor “B” Circuit
  • P041B Exhaust Gas Recirculation Temperature Sensor “B” Circuit Range/Performance
  • P041C Exhaust Gas Recirculation Temperature Sensor “B” Circuit Low
  • P041D Exhaust Gas Recirculation Temperature Sensor “B” Circuit High
  • P041E Exhaust Gas Recirculation Temperature Sensor “B” Circuit Intermittent/Erratic
  • P041F Secondary Air Injection System Switching Valve “A” Circuit Low
  • P0420 Catalyst System Efficiency Below Threshold (Bank 1)

What Does OBD-II Fault Code P0420 Mean?

OBD-II Code P0420 is defined as a Catalyst System Efficiency Below Threshold

P0420 Symptoms

  • Check Engine Light will illuminate
  • In most cases, there are no adverse conditions noticed by the driver
  • In some cases, there may be some performance problems noticed by the driver such as a lack of power from a restricted and/or damaged Catalytic Converter

Common Problems That Trigger the P0420 Code

  • Inefficient Catalytic Converter(s)
  • Defective Front or Rear Oxygen Sensor(s)
  • Misfiring engines

Common Misdiagnoses

  • Oxygen Sensors

Polluting Gases Expelled

  • HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
  • CO (Carbon Monoxide): Partially burned fuel that is an odorless and deadly poisonous gas
  • NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog

Notes

  • Volkswagen , Audi , Dodge and Toyota have extended their catalytic converter coverage on many of their vehicles. To find out more about this information on RepairPal.com, enter P0420 followed by your vehicle make in the search bar above, for example, P0420 Audi.
  • Most Toyota vehicles need an OEM Catalyst, especially if there is a Catalyst-related software update required. Toyota vehicles usually re-set the P0420 code unless an OEM catalyst is used as a replacement. It is common for mechanics to replace all the Oxygen sensors only to find that the Toyota vehicle required an OEM Catalyst.
  • Most of the aftermarket Converter companies are re-working their designs so they can be certified for use in OBD-II vehicles in California
  • If you call a dealer to inquire about the warranty, have your VIN code ready to be checked in the manufacturer database, if you just call to ask about what is covered, typically the dealership will only tell you the minimal coverage. You need to be proactive and ask a Service Writer, not a phone receptionist, to check your VIN code for the most up to date warranty information.

The Basics

The Catalytic Converter looks like a muffler. It is typically a stainless steel housing over a ceramic honeycomb core. The catalyst itself is made of platinum, palladium, or rhodium, all rare metals, which is why Catalytic Converters are so expensive. These elements reduce the toxicity of harmful exhaust gases that are expelled from the tail pipe. Catalytic converters are quite efficient, but if engine maintenance is neglected or an engine is allowed to “run rough,” damage could occur, resulting in costly repairs. To replace the Catalytic Converter, the vehicle is raised to gain access to its underside. The converter is removed from the exhaust system and the new Catalytic Converter is installed.

Want to Learn More?

The Catalytic Converter is a sophisticated after-burning device designed to complete combustion of the exhaust gases that pass through it. It is a stainless steel container with an inlet and outlet pipe that looks similar to a muffler. Inside, the Catalytic Converter is a ceramic monolithic structure that has honeycomb-like passages running though it. This structure has several sections called beds that are thinly coated with rare metals, which react with the compounds in the exhaust gases to complete the combustion process, thereby cleaning the exhaust of harmful emissions.

  • The first section of the Catalytic Converter is called the reduction bed and is coated with rhodium. It is called the reduction bed because its purpose is to reduce the NOx gases back into harmless nitrogen and oxygen.
  • The next section of the Catalytic Converter is the oxygen storage bed, which is coated with cerium. Its purpose is to maintain an ideal level of oxygen for use by the rear of the converter. It does this by storing and releasing the oxygen that gets released from the reduction of NOx in the previous reduction bed.
  • The oxygen is then available for use in the final oxidizing bed, which is coated with platinum and palladium. The purpose of the oxidizing bed is to complete the combustion of CO by adding oxygen. The oxidizing bed also uses oxygen to burn any of the raw HCs that still remain in the exhaust gases.

P0420 Diagnostic Theory for Shops and Technicians

The P0420 code is set when the Catalyst monitor sees a decrease in voltage from the rear Monitoring Oxygen Sensor(s) and an increase in switching activity—from rich to lean to rich, etc.—that closely resembles the front Oxygen Sensor(s) during the time the computer is activating the Catalytic Converter monitor test. The voltage threshold is usually a minimum of 650 millivolts, which indicates a low level of oxygen. When the voltage goes too far below the 650 millivolt minimum, it indicates a higher level of oxygen. This means that not all of the oxygen is being consumed by the combustion process or by the afterburning effect of the Catalytic Converter. When the oxygen level gets too high, it means that the Cerium or Oxygen storage bed has degraded to the point where it is no longer able to store oxygen created by the reduction of NOx (nitrogen and oxygen). This oxygen is essential for the rear Oxidation bed to complete the conversion of CO into CO2 and HCs into H20 and CO2.

Common Tests for Diagnosis of the P0420 Code

  • Retrieve the code and write down the freeze frame information to be used as a baseline to test and verify any repair.
  • If there are any misfires, ignition, fuel and/or intake problems, these must be repaired before the Catalyst code is addressed. Any misfire, ignition, and/or fuel system problem will quickly ruin a Catalyst. They are often the cause for code in the first place.
  • Test drive the vehicle at or near the freeze frame conditions to verify that the rear Catalyst Monitoring Oxygen sensor is either mirroring the front Oxygen sensor and/or is not reaching the 650 millivolt threshold during 55–60 MPH cruise conditions. If either of theses conditions can be easily verified, then the Catalytic Converter is defective.
  • If there is any doubt about the condition of the front and/or rear Oxygen sensors, then check the Mode 6 data for all the Oxygen sensor monitor tests. If any of the front or rear Oxygen sensors barely pass their Mode 6 tests, then clear all codes and perform a drive cycle to see how well the front and rear Oxygen sensors pass their Mode 6 tests. They need to pass the Mode 6 tests with flying colors or they will confuse the OBD-II diagnostic software and possibly trigger a false code P0420. This is an important concept because if the front Oxygen sensor is slow and barely passes its monitor tests, it can fool the computer into thinking that the Catalyst has failed because the computer just watches how closely the switching speed of the front Oxygen sensor compares to the switching speed of the rear Monitoring Oxygen sensor. If the rear Monitoring Oxygen sensor is losing bandwidth and not able to easily reach the 650 millivolt threshold—but still barely passes its monitor tests—then it, too, can fool the computer into setting a P0420 code.
  • If the Catalyst has failed, be sure to check for any software updates for the powertrain computer. Many of the OBD II-equipped vehicles require software updates whenever the Catalyst is replaced.

  • P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)
  • P0422 Main Catalyst Efficiency Below Threshold (Bank 1)
  • P0423 Heated Catalyst Efficiency Below Threshold (Bank 1)
  • P0424 Heated Catalyst Temperature Below Threshold (Bank 1)
  • P0425 Catalyst Temperature Sensor (Bank 1, Sensor 1)
  • P0426 Catalyst Temperature Sensor Range/Performance (Bank 1, Sensor 1)
  • P0427 Catalyst Temperature Sensor Low (Bank 1, Sensor 1)
  • P0428 Catalyst Temperature Sensor High (Bank 1, Sensor 1)
  • P0429 Catalyst Heater Control Circuit (Bank 1)
  • P042A Catalyst Temperature Sensor Circuit (Bank 1 Sensor 2)
  • P042B Catalyst Temperature Sensor Circuit Range/Performance (Bank 1 Sensor 2)
  • P042C Catalyst Temperature Sensor Circuit Low (Bank 1 Sensor 2)
  • P042D Catalyst Temperature Sensor Circuit High (Bank 1 Sensor 2)
  • P042E Exhaust Gas Recirculation “A” Control Stuck Open
  • P042F Exhaust Gas Recirculation “A” Control Stuck Closed
  • P0430 Catalyst System Efficiency Below Threshold (Bank 2)
  • P0431 Warm Up Catalyst Efficiency Below Threshold (Bank 2)
  • P0432 Main Catalyst Efficiency Below Threshold (Bank 2)
  • P0433 Heated Catalyst Efficiency Below Threshold (Bank 2)
  • P0434 Heated Catalyst Temperature Below Threshold (Bank 2)
  • P0435 Catalyst Temperature Sensor Circuit Malfunction (Bank 2, Sensor 1)
  • P0436 Catalyst Temperature Sensor Circuit Range/Performance (Bank 2, Sensor 1)
  • P0437 Catalyst Temperature Sensor Circuit Low (Bank 2, Sensor 1)
  • P0438 Catalyst Temperature Sensor Circuit High (Bank 2, Sensor 1)
  • P0439 Catalyst Heater Control Circuit (Bank 2)
  • P043A Catalyst Temperature Sensor Circuit (Bank 2 Sensor 2)
  • P043B Catalyst Temperature Sensor Circuit Range/Performance Bank 2 Sensor 2)
  • P043C Catalyst Temperature Sensor Circuit Low (Bank 2 Sensor 2)
  • P043D Catalyst Temperature Sensor Circuit High (Bank 2 Sensor 2)
  • P043E Evaporative Emission System Leak Detection Reference Orifice Low Flow
  • P043F Evaporative Emission System Leak Detection Reference Orifice High Flow
  • P0440 Evaporative Emission Control System Malfunction

What Does OBD-II Fault Code P0440 Mean?

OBD-II Code P0440 is defined as a Evaporative System Malfunction, Large Leak

Symptoms

  • Check Engine Light will illuminate
  • In most cases, there are no adverse conditions noticed by the driver
  • In some cases, there may be a noticeable fuel odor caused by the release of fuel vapors

Common Problems That Trigger the P0440 Code

  • Missing fuel cap
  • Defective or damaged fuel cap
  • Distorted or damaged Fuel Tank Filler Neck
  • Torn or punctured Evaporative system hose(s)
  • Defective Fuel Tank Sending Unit gasket or seal
  • Split or damaged Carbon Canister
  • Defective Evaporative Vent Valve and/or Evaporative Purge Valve
  • Defective or damaged fuel tank

Common Misdiagnoses

  • Fuel cap
  • Evaporative Purge Valve
  • Evaporative Vent Valve

Polluting Gases Expelled

  • HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog

The Basics

The evaporative control (EVAP) system captures any raw fuel evaporating from the fuel storage system (e.g. the fuel tank, filler neck, and fuel cap). Under precise operating conditions—dictated by engine temperature, speed, and load—the EVAP system stores and purges these captured fuel vapors back into the combustion process.

Want to Learn More?

The EVAP system is designed not only to capture, store, and purge any raw fuel vapors that leak from areas in the Fuel Storage system, but also to run a series of self-tests that confirm or deny the operational and vapor holding ability of the system. This is an important task because at least 20 percent of vehicle-produced air pollution originates from malfunctioning Vehicle Fuel Storage systems.

There are many ways to “leak test” the EVAP system, but most perform the leak test when the vehicle is sitting (like over night) or during the initial start-up after the vehicle has been sitting over night. The EVAP system’s operational performance is also tracked by the Powertrain Computer by reading the change in the oxygen sensor voltages and short term fuel trim whenever the stored vapors are released or “purged” back into the combustion process. These values should indicate that fuel is being added to the system and that the overall mixture is getting richer. The purging process occurs when the vehicle is under acceleration, which is when most vehicles require additional fuel.

P0440 Diagnostic Theory for Shops and Technicians

The P0440 code indicates that there is a large leak in the EVAP system, but this is somewhat misleading. What the code really indicates is that the EVAP system will not create a significant vacuum when it performs its leak test, as monitored by the Fuel Tank Pressure Sensor.

Here is how the evaporative leak test is performed by the Powertrain Computer:

  1. When the leak test is performed, the vehicle must have been sitting for at least four to eight hours so that the engine temperature and outside air temperature are identical. There must also be between 15 and 85 percent fuel in the tank—this is to provide a baseline for the test since gasoline and diesel are volatile fluids that expand and vaporize easily with warm temperatures.
  2. When the leak test initiates, the Vapor Canister Vent Valve is closed to prevent any fresh air from entering the EVAP system.
  3. The Purge Valve is opened, which allows the engine to create a vacuum in the EVAP system.
  4. After a specified time interval—usually about ten seconds—the Purge Valve is shut off and the vacuum level in the system is measured by the Fuel Tank Pressure Sensor.
  5. Finally, a countdown initiates, which measures the rate at which the vacuum decays in the system. If the vacuum decays much faster than the specified rate or if no amount of vacuum is reached on two consecutive tests, then the Powertrain Computer will fail the EVAP system for a gross leak and trigger the P0440 code.

Common Tests for the Evaporative System

  • Retrieve the code and write down the freeze frame information to be used as a baseline to test and verify any repair.
  • Perform a careful and close visual inspection of all accessible hoses and components in the EVAP system for any signs of damage or degradation.
  • Using a scan tool, pay very close attention to the Fuel Tank Pressure readings. Does the Fuel Tank Pressure Sensor work properly? If it doesn’t, the system will think that no pressure or vacuum is being created when the EVAP monitor is performed when, in fact, there is a pressure/vacuum being created that Fuel Tank Pressure Sensor is unable to read. The Fuel Tank Pressure Sensor is the primary feedback sensor that the Powertrain Computer relies on for the leak test data each time the EVAP monitor is run.
  • Inspect and test the fuel cap to determine how well it fits onto the Fuel Tank Filler Neck. Make sure the Fuel Cap Seal isn’t dry or cracked. If the cap will not seal or hold vacuum/pressure, then it can trigger the P0440 code.
  • Verify that the Purge Valve and the Vent Valve work properly and hold vacuum for a sustained amount of time—at least thirty to sixty seconds. If either one of these valves function improperly, the system will not develop and/or hold the proper amount of vacuum.
  • If all the components seem to function properly, then perform another smoke test of the entire EVAP system. This will usually root out any leaks that are hidden behind and/or under components of the vehicle. Pay close attention to the Fuel Tank Filler Neck, the Carbon Canister, and the Fuel Tank itself, especially where the Fuel Pump and Fuel Level Sending unit are located and sealed. Occasionally when a Fuel Pump is replaced, the seal isn’t replaced or properly installed. This can cause small leaks in the system. You might have to remove the rear seats to further inspect and pinpoint the source of a Fuel Tank leak.

  • P0441 Evaporative Emission Control System Incorrect Purge Flow
  • P0442 Evaporative Emission Control System Leak Detected (small leak)

What Does OBD-II Fault Code P0442 Mean?

OBD-II Code P0442 is defined as a Evaporative System Malfunction, Small Leak

Symptoms

  • Check Engine Light will illuminate
  • In most cases, there are no adverse conditions noticed by the driver
  • In some cases, there may be a noticeable fuel odor caused by the release of fuel vapors

Common Problems That Trigger the P0442 Code

  • Defective or damaged fuel cap
  • Distorted or damaged Fuel Tank Filler Neck
  • Small tear or puncture in the Evaporative system hose(s) and/or Carbon Canister
  • Defective Fuel Tank Sending Unit gasket or seal
  • Small split in a seam of the Carbon Canister
  • Defective Evaporative Vent Valve and/or Evaporative Purge Valve
  • Defective or damaged Fuel Tank
  • Defective Fuel Tank Pressure Sensor
  • Defective Leak Detection Pump
  • Slightly loose and/or worn clamps or hardened O-rings anywhere in the EVAP system

Common Misdiagnoses

  • Fuel cap
  • Evaporative Purge Valve
  • Evaporative Vent Valve

Polluting Gases Expelled

HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog

The Basics

The evaporative control (EVAP) system captures any raw fuel evaporating from the fuel storage system (e.g. the fuel tank, filler neck, and fuel cap). Under precise operating conditions—dictated by engine temperature, speed, and load—the EVAP system stores and purges these captured fuel vapors back into the combustion process.

Want to Learn More?

The EVAP system is designed not only to capture, store, and purge any raw fuel vapors that leak from areas in the Fuel Storage system, but also to run a series of self-tests that confirm or deny the operational and vapor holding ability of the system. This is an important task because at least 20 percent of vehicle-produced air pollution originates from malfunctioning Vehicle Fuel Storage systems.

There are many ways to “leak test” the EVAP system, but most perform the leak test when the vehicle is sitting (like overnight) or during the initial start-up after the vehicle has been sitting overnight. The EVAP system’s operational performance is also tracked by the Powertrain Computer by reading the change in the oxygen sensor voltages and short term fuel trim whenever the stored vapors are released or “purged” back into the combustion process. These values should indicate that fuel is being added to the system and that the overall mixture is getting richer. The purging process occurs when the vehicle is under acceleration, which is when most vehicles require additional fuel.

P0442 Diagnostic Theory for Shops and Technicians

The P0442 code indicates that there is a small leak in the EVAP system, but this is somewhat misleading. What the code really indicates is that the EVAP system will not hold a specified level of vacuum for a specified amount of time when it performs its leak test.

Here is how the evaporative leak test is performed by the Powertrain Computer:

1. When the leak test is performed, the vehicle must have been sitting for at least four to eight hours so that the engine temperature and outside air temperature are identical. There must also be between 15 and 85 percent fuel in the tank—this is to provide a baseline for the test since gasoline and diesel are volatile fluids that expand and vaporize easily with warm temperatures.

2. When the leak test initiates, the Vapor Canister Vent Valve is closed to prevent any fresh air from entering the EVAP system. The Purge Valve is also sealed off.

3. The Leak Detection Pump operates to build a vacuum in the entire Evaporative System (see the Leak Detection Pump information below). After a specified time interval—usually about ten seconds—the Purge Valve is shut off and the vacuum level in the system is measured by the Fuel Tank Pressure Sensor.

4. Finally, a countdown initiates, which measures the rate at which the vacuum decays in the system. If the vacuum decays faster than the specified rate on two successive tests, then the Powertrain Computer will fail the EVAP system and trigger the P0442 code. Most modern EVAP systems will fail the leak test with a pin-sized hole anywhere in the EVAP system, which amounts to 0.020 of an inch or a ½ millimeter.

Two Other Commonly Used Variations of Evaporative System Leak Test

The Leak Detection Pump (LDP) uses Engine Vacuum to operate a bellows-like pump to build vacuum in the EVAP system once the Evaporative Vent Valve has sealed the system. The LDP has a diaphragm that changes shape as vacuum builds. When the desired amount of vacuum has been reached, the diaphragm opens a set of electrical contacts that disables the LDP and stops the vacuum from building any further. Then the system starts a timer and monitors how long it takes for the diaphragm to relax and the electrical contacts to close. If the diaphragm relaxes in less than the required amount of time and the points touch too early on two consecutive tests, a code P0442 is set by the Powertrain Computer. The LDP system is common on Chrysler/Jeep and many European vehicles.

The Stationary or Sitting Evaporative Leak Test is performed when the vehicle is sitting. The test uses changes in the Fuel Tank Pressure Sensor data to determine whether or not there is an EVAP system Leak. Once the vehicle is shut off for a predetermined amount of time, the Powertrain Computer closes the Evaporative Vent Valve. Any pressure changes in the Fuel Tank Pressure are closely monitored. Under normal circumstances, the pressure inside the Fuel Tank should decrease slowly as the fuel cools off. If the pressure falls off a little faster than the maximum allowable rate for two consecutive tests, the system will set a code P0442. This type of system is used on many GM and Ford vehicles.

Note: In very hot climates, the EVAP system might never run its monitor because when air temperatures stay over or around 100 degrees, the fuel becomes too volatile, making it impossible for any EVAP system to perform an accurate leak test.

Common Tests for the Evaporative System

  • Retrieve the code and write down the freeze frame information to be used as a baseline to test and verify any repair. If there are any other EVAP system codes, make special note of those as well, as they may be triggering the P0442. It is important to address these codes before you attempt to repair the P0442. Purge Valve or Vent Valve codes (P0446, P0443) can trigger a P0442. If the Vent Valve or Purge Valve is not functioning correctly, it may lead to a small leak that will set the P0442. The same applies to any Fuel Tank Pressure Sensor codes (P0451, P0452) or Leak Detection Pump codes (P1495).
  • Perform a careful and close visual inspection of all accessible hoses and components in the EVAP system for any signs of damage or degradation.
  • Using a scan tool, pay very close attention to the Fuel Tank Pressure readings. Does the Fuel Tank Pressure Sensor work properly? If it doesn’t, the system will think that no pressure or vacuum is being created when the EVAP monitor is performed when, in fact, there is a pressure/vacuum being created that Fuel Tank Pressure Sensor is unable to read. The Fuel Tank Pressure Sensor is the primary feedback sensor that the Powertrain Computer relies on for the leak test data each time the EVAP monitor is run.
  • Inspect and test the fuel cap to determine how well it fits onto the Fuel Tank Filler Neck. Make sure the Fuel Cap Seal isn’t dry or cracked. If the cap will not seal or hold vacuum/pressure, then it can trigger the P0442 code.
  • Verify that the Purge Valve and the Vent Valve work properly and hold vacuum for a sustained amount of time—at least thirty to sixty seconds with no decay. If either one of these valves function improperly, the system will not develop and/or hold the proper amount of vacuum. Energize both the Purge Valve and Vent Valve several times to test their vacuum-holding ability during and after each time they are energized. It is not uncommon for these devices to fail on an intermittent basis
  • Perform an “in bay” Leak Test with a bi-directional scan tool and track how well the Leak Detection Pump performs. You may have to isolate the Leak Detection Pump by pinching off the Purge and Vent Valve. In some cases, a manual Leak Detection Pump performance test is needed—this can be done by manually energizing the contact points on the Leak Detection Pump.
  • If all the components seem to function properly, then perform another smoke test of the entire EVAP system. This will usually root out any leaks that are hidden behind and/or under components of the vehicle. Pay close attention to the Fuel Tank Filler Neck, the Carbon Canister, and the Fuel Tank itself, especially where the Fuel Pump and Fuel Level Sending unit are located and sealed. Occasionally when a Fuel Pump is replaced, the seal isn’t replaced or properly installed. This can cause small leaks in the system. You might have to remove the rear seats to further inspect and pinpoint the source of a Fuel Tank leak.

  • P0443 Evaporative Emission Control System Purge Control Valve Circuit
  • P0444 Evaporative Emission Control System Purge Control Valve Circuit Open
  • P0445 Evaporative Emission Control System Purge Control Valve Circuit Shorted
  • P0446 Evaporative Emission Control System Vent Control Circuit Malfunction
  • P0447 Evaporative Emission Control System Vent Control Circuit Open
  • P0448 Evaporative Emission Control System Vent Control Circuit Shorted
  • P0449 Evaporative Emission Control System Vent Valve/Solenoid Circuit Malfunction
  • P044A Exhaust Gas Recirculation Sensor “C” Circuit
  • P044B Exhaust Gas Recirculation Sensor “C” Circuit Range/Performance
  • P044C Exhaust Gas Recirculation Sensor “C” Circuit Low
  • P044D Exhaust Gas Recirculation Sensor “C” Circuit High
  • P044E Exhaust Gas Recirculation Sensor “C” Circuit Intermittent/Erratic
  • P044F Secondary Air Injection System Switching Valve “A” Circuit High
  • P0450 Evaporative Emission Control System Pressure Sensor Malfunction
  • P0451 Evaporative Emission Control System Pressure Sensor Range/Performance
  • P0452 Evaporative Emission Control System Pressure Sensor Low Input
  • P0453 Evaporative Emission Control System Pressure Sensor High Input
  • P0454 Evaporative Emission Control System Pressure Sensor Intermittent
  • P0455 Evaporative Emission Control System Leak Detected (gross leak)

What Does OBD-II Fault Code P0455 Mean?

OBD-II Code P0455 is defined as a Evaporative System Malfunction, Gross Leak

Symptoms

  • Check Engine Light will illuminate
  • In most cases, there are no adverse conditions noticed by the driver
  • In some cases, there may be a noticeable fuel odor caused by the release of fuel vapors

Common Problems That Trigger the P0455 Code

  • Missing fuel cap
  • Defective or damaged fuel cap
  • Distorted or damaged Fuel Tank Filler Neck
  • Torn or punctured Evaporative system hose(s)
  • Defective Fuel Tank Sending Unit gasket or seal
  • Split or damaged Carbon Canister
  • Defective Evaporative Vent Valve and/or Evaporative Purge Valve
  • Defective or damaged fuel tank
  • Defective Fuel Tank Pressure Sensor

Common Misdiagnoses

  • Fuel cap
  • Evaporative Purge Valve
  • Evaporative Vent Valve

Polluting Gases Expelled

  • HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog

The Basics

The evaporative control (EVAP) system captures any raw fuel evaporating from the fuel storage system (e.g. the fuel tank, filler neck, and fuel cap). Under precise operating conditions—dictated by engine temperature, speed, and load—the EVAP system stores and purges these captured fuel vapors back into the combustion process.

Want to Learn More?

The EVAP system is designed not only to capture, store, and purge any raw fuel vapors that leak from areas in the Fuel Storage system, but also to run a series of self-tests that confirm or deny the operational and vapor holding ability of the system. This is an important task because at least 20 percent of vehicle-produced air pollution originates from malfunctioning Vehicle Fuel Storage systems.

There are many ways to “leak test” the EVAP system, but most perform the leak test when the vehicle is sitting (like overnight) or during the initial start-up after the vehicle has been sitting over night. The EVAP system’s operational performance is also tracked by the Powertrain Computer by reading the change in the oxygen sensor voltages and short term fuel trim whenever the stored vapors are released or “purged” back into the combustion process. These values should indicate that fuel is being added to the system and that the overall mixture is getting richer. The purging process occurs when the vehicle is under acceleration, which is when most vehicles require additional fuel.

P0455 Diagnostic Theory for Shops and Technicians

The P0455 code indicates that there is a large leak in the EVAP system, but this is somewhat misleading. What the code really indicates is that the EVAP system will not create a significant vacuum when it performs its leak test, as monitored by the Fuel Tank Pressure Sensor.

Here is how the evaporative leak test is performed by the Powertrain Computer:

  1. When the leak test is performed, the vehicle must have been sitting for at least four to eight hours so that the engine temperature and outside air temperature are identical. There must also be between 15 and 85 percent fuel in the tank—this is to provide a baseline for the test since gasoline and diesel are volatile fluids that expand and vaporize easily with warm temperatures.
  2. When the leak test initiates, the Vapor Canister Vent Valve is closed to prevent any fresh air from entering the EVAP system.
  3. The Purge Valve is opened, which allows the engine to create a vacuum in the EVAP system.
  4. After a specified time interval—usually about ten seconds—the Purge Valve is shut off and the vacuum level in the system is measured by the Fuel Tank Pressure Sensor.
  5. Finally, a countdown initiates, which measures the rate at which the vacuum decays in the system. If the vacuum decays much faster than the specified rate or if no amount of vacuum is reached on two consecutive tests, then the Powertrain Computer will fail the EVAP system for a gross leak and trigger the P0455 code.

Common Tests for the Evaporative System

  • The P0455 code is somewhat misleading because the problem may not be a large/gross leak at all. Many systems trigger this code if there is no EVAP flow detected, which is tracked by changes in Short Term Fuel Trim and Fuel Tank Pressure Sensor data. For example, if the Purge Valve is shorted and never closes, it can trigger a P0455. Be ready to think outside of the box when tracking down the cause of a P0455.
  • Retrieve the code and write down the freeze frame information to be used as a baseline to test and verify any repair.
  • Perform a pressurized smoke test. During the test, perform a careful and close examination of the visible hoses, fuel filler neck, installed filler cap, fuel tank, vent valve, purge valve, and vapor holding canister. Open the Throttle Body to make sure there isn’t an internal leak that is flowing smoke into the intake manifold. (Be sure to close off the vent valve during the smoke test! If possible, use tape so you don’t overwork the electrical portion of the Vent Solenoid by having it energized for too long.)
  • Run an additional smoke test while using the scan tool live data stream feature with the Fuel Tank Pressure Sensor PID in plain view. As the test inserts smoke into the fuel storage system, the Fuel Tank Pressure readings should increase. If the pressure readings do not increase, the system will think that no pressure or vacuum is being created when the EVAP monitor is performed when, in fact, there is a pressure/vacuum being created that Fuel Tank Pressure Sensor is unable to read. The Fuel Tank Pressure Sensor is the primary feedback sensor that the Powertrain Computer relies on for the leak test data each time the EVAP monitor is run.
  • Inspect and test the fuel cap to determine how well it fits onto the Fuel Tank Filler Neck. If the cap will not seal or hold vacuum/pressure, then it can trigger the P0455 code.
  • Verify that the Purge Valve and the Vent Valve work properly and hold vacuum for a sustained amount of time—at least thirty to sixty seconds. If either one of these valves function improperly, the system will not develop and/or hold the proper amount of vacuum. You may have to remove and bench test them. Also be sure to measure the electrical resistance of the solenoids to be sure they are in spec.
  • If all the components seem to function properly, then perform another smoke test of the entire EVAP system, but this time, use your sense of smell. Go around the entire system to see if you can smell any fuel odor. In some cases, the smoke will exit in a manner that is invisible, but there will be evidence of a fuel odor that will lead you to the problem area. This area may be completely hidden by the frame, fuel tank, etc.
  • If all tests fail, clear all the codes and perform a drive cycle test drive to make sure that the code re-sets are what are the freeze frame data points are referring to.

  • P0456 Evaporative Emissions System Small Leak Detected
  • P0457 Evaporative Emission Control System Leak Detected
  • P0458 Evaporative Emission System Purge Control Valve Circuit Low
  • P0459 Evaporative Emission System Purge Control Valve Circuit High
  • P045A Exhaust Gas Recirculation “B” Control Circuit
  • P045B Exhaust Gas Recirculation “B” Control Circuit Range/Performance
  • P045C Exhaust Gas Recirculation “B” Control Circuit Low
  • P045D Exhaust Gas Recirculation “B” Control Circuit High
  • P045E Exhaust Gas Recirculation “B” Control Stuck Open
  • P045F Exhaust Gas Recirculation “B” Control Stuck Closed
  • P0460 Fuel Level Sensor Circuit Malfunction
  • P0461 Fuel Level Sensor Circuit Range/Performance
  • P0462 Fuel Level Sensor Circuit Low Input
  • P0463 Fuel Level Sensor Circuit High Input
  • P0464 Fuel Level Sensor Circuit Intermittent
  • P0465 Purge Flow Sensor Circuit Malfunction
  • P0466 Purge Flow Sensor Circuit Range/Performance
  • P0467 Purge Flow Sensor Circuit Low Input
  • P0468 Purge Flow Sensor Circuit High Input
  • P0469 Purge Flow Sensor Circuit Intermittent
  • P046A Catalyst Temperature Sensor 1/2 Correlation (Bank 1)
  • P046B Catalyst Temperature Sensor 1/2 Correlation (Bank 2)
  • P046C Exhaust Gas Recirculation Sensor “A” Circuit Range/Performance
  • P046D Exhaust Gas Recirculation Sensor “A” Circuit Intermittent/Erratic
  • P046E Exhaust Gas Recirculation Sensor “B” Circuit Range/Performance
  • P046F Exhaust Gas Recirculation Sensor “B” Circuit Intermittent/Erratic
  • P0470 Exhaust Pressure Sensor “A” Circuit
  • P0471 Exhaust Pressure Sensor “A” Circuit Range/Performance
  • P0472 Exhaust Pressure Sensor “A” Circuit Low
  • P0473 Exhaust Pressure Sensor “A” Circuit High
  • P0474 Exhaust Pressure Sensor “A” Circuit Intermittent
  • P0475 Exhaust Pressure Control Valve “A”
  • P0476 Exhaust Pressure Control Valve “A” Range/Performance
  • P0477 Exhaust Pressure Control Valve “A” Low
  • P0478 Exhaust Pressure Control Valve “A” High
  • P0479 Exhaust Pressure Control Valve “A” Intermittent
  • P047A Exhaust Pressure Sensor “B” Circuit
  • P047B Exhaust Pressure Sensor “B” Circuit Range/Performance
  • P047C Exhaust Pressure Sensor “B” Circuit Low
  • P047D Exhaust Pressure Sensor “B” Circuit High
  • P047E Exhaust Pressure Sensor “B” Circuit Intermittent/Erratic
  • P047F Exhaust Pressure Control Valve “A” Stuck Open
  • P0480 Cooling Fan I Control Circuit Malfunction
  • P0481 Cooling Fan 2 Control Circuit Malfunction
  • P0482 Cooling Fan 3 Control Circuit Malfunction
  • P0483 Cooling Fan Rationality Check Malfunction
  • P0484 Cooling Fan Circuit Over Current
  • P0485 Cooling Fan Power/Ground Circuit Malfunction
  • P0486 Exhaust Gas Recirculation Sensor “B” Circuit
  • P0487 Exhaust Gas Recirculation Throttle Control Circuit “A” Open
  • P0488 Exhaust Gas Recirculation Throttle Control Circuit “A” Range/Performance
  • P0489 Exhaust Gas Recirculation “A” Control Circuit Low
  • P048A Exhaust Pressure Control Valve “A” Stuck Closed
  • P048B Exhaust Pressure Control Valve Position Sensor/Switch Circuit
  • P048C Exhaust Pressure Control Valve Position Sensor/Switch Circuit Range/Performance
  • P048D Exhaust Pressure Control Valve Position Sensor/Switch Circuit Low
  • P048E Exhaust Pressure Control Valve Position Sensor/Switch Circuit High
  • P048F Exhaust Pressure Control Valve Position Sensor/Switch Circuit Intermittent/Erratic
  • P0490 Exhaust Gas Recirculation “A” Control Circuit High
  • P0491 Secondary Air Injection System Insufficient Flow Bank 1
  • P0492 Secondary Air Injection System Insufficient Flow Bank 2
  • P0493 Fan Overspeed
  • P0494 Fan Speed Low
  • P0495 Fan Speed High
  • P0496 EVAP Flow During A Non-Purge Condition
  • P0497 Evaporative Emission System Low Purge Flow
  • P0498 Evaporative Emission System Vent Valve Control Circuit Low
  • P0499 Evaporative Emission System Vent Valve Control Circuit High