OBD Engine Codes – The Check Engine Light Is Only The Messenger

OBD Engine Codes - The Check Engine Light Is Only The Messenger
OBD Engine Codes - The Check Engine Light Is Only The Messenger

So, OBD Engine Codes, or a check engine light, cannot be fixed by; simply resetting it or disconnecting the battery.

In other words, the OBD Engine Codes, and dreaded check engine light will return! However, stay cool, the check engine light is only the messenger.

When this system identifies an issue; it turns on the check engine light and records OBD engine codes.

Because, it is simply doing it’s very important job; letting you know that your vehicle, isn’t operating at top efficiency.

Furthermore, the check engine light is not only for, the vehicle’s emission system. This light informs the operator when there is a problem; anywhere in the vehicles, electronic engine control system.

The OBD Engine Codes System, Basically Includes:

  • sensors
  • solenoids
  • valves
  • actuators

Consequently, your vehicle needs these and many more to operate correctly. So, to troubleshoot, repair and maintain your vehicle; you’ll need diagnostic repair information, that is specific to your vehicle.

Check Engine Light
Check Engine Light

But, with only a few basic tools, a little patience and some mechanical aptitude; you can pinpoint and repair most of these concerns yourself.

So, How Do I Read The OBD Engine Codes !

How Do I Read The Codes
How Do I Read The Codes

Firstly, the first character identifies the system, related to the trouble OBD Engine Codes.

  • P = (Powertrain)
  • B = (Body)
  • C = (Chassis)
  • U = (Network Communication)

Secondly, the second digit identifies, whether the OBD Engine Code is a generic code (same on all OBD-II equipped vehicles); or a manufacturer specific code.

  • 0 = (Standardized Code ISO/SAE) Generic (this is the digit zero — not the letter “O”)
  • 1 = (manufacturer specific OBD Codes)

While, the third digit, denotes the type of sub system, that pertains to the OBD Engine Code.

  1. (Secondary Air Injection System) Emission Management (Fuel or Air)
  2. (Fuel System) Injector Circuit (Fuel or Air)
  3. ( Ignition System) or Misfire
  4. (Exhaust Monitoring System) Emission Control
  5. (Idle Speed Control) Vehicle Speed
  6. (ECU) Computer & Output Circuit
  7. (Transmission System)
  8. (Transmission System)

9= SAE Reserved

0= SAE Reserved

Finally, OBD Codes-4th and 5th, these digits are variable, and relate to a specific problem.

OBD Codes Reader
OBD Codes Reader

OBD Code Categories

P0100-P0199 – Fuel and Air Metering. So, these will be things like the mass airflow sensor and throttle body.

P0200-P0299 – Fuel and Air Metering (Injector Circuit). Consequently, these codes would be for things involving the fuel injectors.

P0300-P0399 – Ignition System or Misfire. So, if there was a bad spark plug or faulty coil you would see one of these codes.

P0400-P0499 – Auxiliary Emissions Controls. Above all, these are the famous (EVAP) system codes.

P0500-P0599 – Vehicle Speed Controls and Idle Control System. Furthermore, the idle air control valve and (VSS) would fall under this category.

P0600-P0699 – Computer Output Circuit. As a result, sometimes these types of codes point to a faulty computer.

P0700-P0999 – Transmission Codes. Finally, simply lets the driver know that there is a fault in the transmission computer; and the TCU needs to be scanned for codes.

So, now you have a better idea of what makes up a Diagnostic Trouble Code. As a result, you can see that every digit has its purpose. Also, you know which system is having the problem. Therefore, just by knowing what the first few digits are.

Diagnostic Trouble Code Reader
Diagnostic Trouble Code Reader

A Short List Of, OBD Codes Definitions And Abbreviations

  • ABS:  Antilock Brake System
  • AC:  Air Conditioning
  • Baro:  Barometric pressure. Usually a sensor.
  • CKP Crankshaft Position
  • CMP:  Camshaft Position
  • CO:  Carbon Monoxide
  • CO2:  Carbon Dioxide
  • DLC:  Data Link Connector
  • DTC:  Diagnostic Trouble Code
  • ECM:  Engine Control Module
  • ECM:  Electronic Control Module
  • ECS:  Emission Control System
  • ECT:  Engine Coolant Temperature
  • ECU:  Electronic Control Module
  • EEC:  Electronic Engine Control
  • EGR:  Exhaust Gas Recirculation
  • EVAP:  Evaporative Emissions
  • FTP:  Fuel Tank Pressure
  • H2O:  Water
  • HO2S:  Heated Oxygen Sensor
  • hp:  Horsepower
  • IAC:  Idle Air Control
  • IAT:  Intake Air Temperature
  • IC:  Ignition Control
  • I/M:  Inspection Maintenance
  • KS:  Knock Sensor
  • MAF:  Mass Airflow Sensor
  • MAP:  Manifold Absolute Pressure
  • MIL: Malfunction Indicator Lamp
  • NOx:  Nitrogen Oxides
  • OBD:  On Board Diagnostics
  • OBD-II:  On Board Diagnostics generation 2
  • PCM:  Powertrain Control Module
  • SES:  Service Engine Soon
  • TCC:  Torque Converter Clutch
  • TDC:  Top Dead Center
  • TP:  Throttle Position
  • TPS:  Throttle Position Sensor
  • TWC:  Three Way Catalyst
  • VCM:  Vehicle Communication Module
  • VSS:  Vehicle Speed Sensor
  • WOT:  Wide Open Throttle


So, OBD engine codes are accessed, by plugging a code reader, into the vehicle’s OBD port. Consequently, these codes provide a mechanic, with information about the system and the conditions; under which the issue was first identified.

However, they can’t provide a clear-cut solution to the actual cause of the problem. Because, the check engine light, is only the messenger. So, to learn more about what your vehicle is trying to tell you; read more on our OBD engine codes page.

Finally, our goal is to provide you with the knowledge; to know what is going on with your vehicle; when the check engine light comes on.

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