Replacement of a good Oxygen Sensor, is a common mistake made by (DIY) mechanics all the time.
So, before replacing any Oxygen Sensor, you must find the real problem first.
First, the Oxygen Sensor is responsible for measuring, how much unburned (O2), is in the exhaust. And, that information is sent to the (ECU), to analyze in real time. Then, the (ECU) knows whether your engine is running, too rich or too lean.
As a result, the (ECU) can make the correct adjustments. Then, figure out what the correct air/fuel ratio should be, for the best engine performance.
The Oxygen Sensor, also known as the (O2) Sensor is a wear item, and does fail over time. So, it is important to remember that today’s vehicles, are controlled by Computers and Sensors. There may be as many as 20 Sensors, feeding information to the (ECU).
So, there are other Sensors, while not directly attached to the (ECU), that do affect the information. Consequently, these Sensors are part of other systems that operate together, to make the engine run efficiently.
All of the systems must be operating correctly for the engine to function properly, and have normal combustion.
What Should We Check When We Have Those, Rich Or Lean Engine Codes
So, if there is too much fuel and not enough air, the engine is said to be “Running Rich”. It will have a gassy or rotten egg smell, from the exhaust. And, give off a burning effect to the eyes, and will make black smoke.
However, if there is too much air and not enough fuel, the engine is said to be “Running Lean”.
The Most Common Issues, For Lean Engine Codes Are:
Vacuum Leaks
- What is a vacuum leak? It’s a leak anywhere between the engine, and the (MAF) Sensor. In most cars, a (MAF) Sensor is installed at the air filter box. The (PCM) calculates how much fuel to inject, based on the (MAF) Sensor readings.
- So, a vacuum leak anywhere between the engine and the (MAF) Sensor, causes “Unmetered” air to enter the system. This causes the actual air flow to be higher, than the (MAF) Sensor measures. As a result, the (PCM) miscalculates the amount of the injected fuel, and the engine runs “Lean”. The term “Lean” means too much air, and too little fuel. The effect of a vacuum leak is more noticeable at idle, when the air flow is lower.
Clogged Filters Or Lines
- Restricted fuel, air and pinched fuel lines. For example, with insufficient air intake, the resulting air/fuel mixture will likely be too rich.
Faulty Sensors
- The failure of a Sensor impacts its proper functioning, and the transmission of information to the (ECU). As a result, this affects your vehicle’s optimal functioning.
Engine Misfires
- The (O2) Sensors only read (O2) content in the exhaust. So, if you have all that unburned fuel from incomplete combustion. Then, you also have, all that unburned (O2). High (O2) content in the exhaust, equals a lean reading, also causing engine misfires.
There are also some other possibilities, such as an internally leaking EGR system.
This will typically set a separate code. A leak in the exhaust system, before the (O2) Sensor will also cause incorrect readings. The only other possibilities are, wiring issues and computer concerns.
The Possible Causes Of, Rich Engine Codes Are:
- A leaking or faulty, fuel injector.
- Fuel injector driver in the computer is shorted, or a wiring short for the injectors. (likely a ground short)
- Leaking or faulty fuel pressure regulator, or a restricted fuel return line.
- A faulty (EVAP) system, bleeding fuel vapors into engine. (not commanded by the computer)
- On newer models, a faulty fuel pump or fuel pump driver module.
- Faulty readings from other Sensors, such as a (MAF) Sensor. You may actually be getting more air than the (MAF) Sensor tells the computer.
- Exhaust leaks, before the Sensor, will cause erratic readings.
The other codes we should address, are those related to the Sensors, located after the catalytic converter. Though these may appear identical to the (O2) Sensor pre-converter. They perform an entirely different task, and are known as, “Monitors”. The only job these Sensors do is, “Monitor” the efficiency of the catalytic converters.
The readings from these Sensors, should be much more stable. And, not fluctuate like the front (O2) Sensors.
The computer compares the readings from, the (O2) Sensor (pre cats) and the “Monitors” (post cat). Then, determines if the catalytic converters are doing their job, and “Cleaning” the exhaust. You never want to replace a “Monitor” for a rich/lean concern, as they have no bearing on these codes.
As the converters begin to fail, you will see the “Monitors” voltage readings, follow the (O2) Sensor readings. Technically these are all “Oxygen Sensors” but it is important to distinguish the difference. So, between pre-converter & post converter Sensors, I find it easiest to stick to calling the back ones “Monitors”.
Why, An Oxygen Sensor May Go Bad
So, the (O2) Sensor can last, up to 100K miles. But, typically you would experience problems, sooner than that. Over time, an (O2) Sensor may become caked with byproducts of combustion. Such as sulfur, lead, fuel additives, and oil ash. This contamination, causes the Sensor to lose its ability, to produce voltage, and send the right signal.
This is critical for maintaining, low emissions and good fuel economy. Sometimes, an (O2) Sensor gets “Lazy” because of old age or contamination. Then, the computer may not be able to adjust the fuel mixture quickly enough, as the engine’s operating conditions change. (O2) Sensors that are failing tend to read lean, which causes the fuel system to run overly rich to compensate.
Signs Of A Bad Oxygen Sensor
In most cases, a bad (O2) Sensor will trigger a (CEL). P0138 and P0135 are some of the codes you may expect to see on a OBD II reader. Other than that, it’s difficult to spot a failing (O2) Sensor. It will inevitably lead to decreased fuel mileage. But, it’s usually not drastic enough, for an average driver to notice. Also, a bad or failing (O2) Sensor, can also cause you to fail your emissions test.
When To Replace The Oxygen Sensor
Always follow the instructions in your owner’s manual, for (O2) Sensor replacement. The Oxygen Sensor is a wear item and does fail over time. This will reduce the level of emissions, your vehicle puts into the atmosphere. And, at the same time, keep your engine running smoothly.
Conclusion
So, what happens to (O2) Sensors is that they tend to become fouled with carbon, and sooty deposits. The element just simply erodes and wears down. Just like the electrode on a spark plug.
Finally, neglecting to replace a bad Oxygen Sensor, will usually result in damage to your catalytic converter.
BY DANNY BENDER
