Which Codes Will This Page Cover?
- P0156 O2 Sensor Circuit – Bank 2 Sensor 2
- P0157 O2 Sensor Circuit Low Voltage
- P0158 O2 Sensor Circuit High Voltage
- P0159 O2 Sensor Circuit Slow Response
- P0160 O2 Sensor Circuit no Activity Detected
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What Is the P0156 Code?
Symptoms
Causes
Seriousness
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The P0156 code has to do with the oxygen sensors that measure the amount of oxygen present in your exhaust and relay it back to the Engine Control Module (ECM). Based on what these measurements come in at, the O2 sensor will fluctuate between low and high voltage measurements, which in turn dictates how much fuel is injected into your engine. The P0156 code sets when Sensor 2 on the Bank 2 side of the engine is malfunctioning.
If the oxygen sensor remains at a low voltage for an extended period, or just simply ceases to emit readings, the P0156 code will be triggered by the ECM. The Sensor 2 in question means that it is the sensor that is located behind your catalytic converter and the Bank 2 side of the engine is the side that does not contain the #1 cylinder. The O2 sensors are critical in the operation of your engine as inaccurate sensors can cause the ECM to add or take away fuel from the motor and cause a myriad of other issues.
More About The P0156 And Its Related Codes
As we’ve stated, the P0156 code refers to the oxygen sensor that is located downstream, or post-catalytic converter, on the Bank 2 side of the engine. The sensor heater allows the O2 sensor to warm up faster than it otherwise would by relying on the exhaust temperature to warm it up. This is important because the sensor needs to warm up for the ECM to allow the engine to achieve closed-loop mode. A closed-loop mode is when the engine receives the correct amount of air and fuel to operate efficiently.
The O2 sensor relays measurements between 0.1 and 0.9 volts to the ECM based on the amount of oxygen it senses in the exhaust. Low readings are closer to 0.1 and indicate that the sensor is noticing more air in the exhaust is running a lean condition. If the condition is present for an extended period (usually more than 20 seconds), the ECM will trigger the P0156 code. The related codes of P0157 and P0159 can also be triggered if the low voltage persists, or if the ECM is not receiving communication from Sensor 2 for extended periods of time. The P0160 code triggers if the communication between the sensor and the ECM ceases completely and no voltage readings are being emitted. Finally, the P0158 code triggers when the sensor reads high voltage, and in turn, a rich exhaust reading. This means not enough air is detected in the exhaust and the ECM will try to make adjustments by lowering the fuel ratio compared to air.
What Are the Symptoms of a P0156 Code?
Most times the very first symptom that accompanies a P0156 code, as well as its related codes, is that your vehicle will have a Check Engine Light immediately set on your dash. This is usually not accompanied by any immediate physical symptoms that you’ll be able to notice. This is because Sensor 2 on the Bank 2 side of the vehicle only inputs to the ECM to monitor the quality of the catalytic converter, so it doesn’t directly control the fuel. However, you can notice excessive fuel consumption from your vehicle after some time since your vehicle will be running on an air and fuel ratio that is not ideal. You can also start noticing excessive smoke coming out of your exhaust if the rich fuel condition continues for a time. Finally, you may notice a rough idle or issues accelerating with any of the P0157-P0160 codes because they are all indicative of a condition that is keeping your vehicle from running on the correct air-to-fuel ratio.
What Are Some Causes of a P0156 Code?
There are a few causes of a P0156 code – and its related codes – triggering and the first of these is that your vehicle may be experiencing gas leaks in the exhaust. As for your oxygen sensors, they are like very small batteries that produce a voltage. When an O2 is failing most times it will be a low voltage condition or lazy fluctuations in the data stream and will cause the P0156 code to show. Your engine may also have air leaks in the intake manifold that is causing less air to pass through the exhaust and, thus, lead to low voltage readings by the oxygen sensor.
Defective fuel injectors can also be the cause of a P0156 code triggering. This can be the case of too much or too little fuel being injected into the combustion chamber. You may also be dealing with broken or defective voltage wires leading to or from the oxygen sensor, or defective wiring harnesses around the sensor. If there are holes in the exhaust located near or around the oxygen sensor this will also cause the P0156 or its related codes to trigger. Engine vacuum leaks are also a cause of codes like the P0158 because they can cause too little air to pass through the exhaust, and induce a rich running condition. Needless to say, all of these codes can cause your vehicle to start having serious physical symptoms.
How Serious Is the P0156 Code?
While there are no immediate symptoms when a P0156 code sets, it is not recommended to drive your car for prolonged periods of time with it set. This is because extended use of your vehicle, while it’s operating on a wrong air and fuel ratio, can cause your engine internals to sustain extensive damage and even break. Your vehicle needs the correct air and fuel ratio to ensure that the combustion process is performing as is intended. So even though these symptoms are unlikely to be felt immediately, we still recommend that you get your vehicle checked out by a qualified service technician as soon as you are presented with the P0156 or its related codes. You should find a qualified service center near you and take your vehicle there as soon as you see this code so that the proper diagnosis and repair can be performed.
Can I Still Drive with a P0156 Code?
Even though we have shown that the P0156 won’t cause immediate damage to your vehicle, we still recommend that you don’t drive your vehicle for extended periods of time with it set. This code may not present any physical symptoms, but the longer you continue to operate your car, the more of a risk you are making for more serious damage to occur. And the repairs that will be needed if your engine’s internals break or stop working can quickly add up. Parts like pistons, valves, and camshafts are vital vehicle components and must work without hindrance, and are thus extremely difficult and costly to replace. This is why you should take your car to an experienced mechanic as soon as you notice the P0156 or its related codes.
How Easy Is It to Diagnose a P0156 Code?
Even though the process for diagnosing a P0156 or its related codes can seem straightforward, it is still best left for experienced technicians with experience diagnosing and repairing these types of issues. The diagnosis process also is going to require tools like voltage readers and advanced scanners that can record freeze frame data and live data readings.
The first step in the diagnosis process is observing the live data from the O2 sensor and the fuel injector to make sure that they are both working properly. The technician will then look to see if the O2 sensor is quickly switching from low to high voltage to learn if you are dealing with a faulty sensor. They will then physically check for any broken or shorted wiring that leads to Sensor 2 and away from the sensor and to the ECM. After this, it’s important to check for any vacuum leaks in the engine or any holes in the exhaust that could potentially indicate that air is leaking from the engine. If there aren’t any of these issues, then the usual diagnosis is that Sensor 2 is defective or broken and should be repaired.
How Difficult Is It to Inspect a P0156 Code?
While the diagnosis process can seem like a light task, it’s important to note that repairing a P0156 issue can be challenging if a poor diagnosis is made. A common mistake is made with replacing the O2 sensor itself without troubleshooting other issues. The oxygen sensor isn’t always the issue and replacing it doesn’t necessarily always solve the problem. This is why it’s important to leave this work to qualified technicians that are certified and have extensive experience with inspecting these issues. They will give consideration to things like wiring, exhaust and vacuum leaks, and issues surrounding the intake or the fuel injectors.
When the technician does reach the root issue of the P0156 code, they will most often repair the shortened, broken, or exposed oxygen sensor wiring. They may also repair the vacuum or exhaust leaks, or replace the fuel injection system entirely if that is the issue. Finally, they will replace the O2 sensor if all other systems are operating as they should be. Because the inspection process is lengthy, it’s not recommended that you undertake this as a DIY project.
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