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When the Check Engine Light turns on, it’s worrisome as there’s little initial indication of the cause. To avoid any potential damage to your vehicle, it's best to avoid driving it until you know the code because doing so can damage the vehicle. If you use an OBD-II scanner or have a professional technician look over your engine and it's displaying a P0155 code, you’re in the right place.
We’ll take you through what a P0155 code is, the symptoms and causes, and how to diagnose the problem.
What Is a P0155 Code?
A P0155 engine code is triggered when your engine’s power control module (PCM) identifies a problem with its connection to your vehicle’s heated oxygen sensors. These sensors are essential for getting your engine up to the appropriate operating speed, so the PCM must get a clear reading. Unfortunately, when your engine throws this code, the PCM experiences too much resistance of an open circuit, which is problematic. In this case, it's usually an issue with the sensor’s heating element.
This becomes a problem because the PCM is actively performing tests on heated O2 sensors to prevent the engine from remaining in an open loop. Essentially, the PCM needs readings from the O2 sensors to adjust the mixture of fuel and air in the cylinders to maximize performance and fuel economy. An engine running in an open loop is an engine that does not adjust the air-to-fuel ratio. While this is fine when an engine begins to warm up, if your motor is in an open loop for too long, it won't run properly and can lead to damage, higher fuel costs, and a failed emissions inspection.
It's also important to note that P0155 is specific to the first sensor in Bank 2 of the engine, which is located ahead of the catalytic converter. Bank 1 is the side of the engine with the first piston, while Bank 2 is the side of the engine with the last piston.
What Are the Symptoms And Causes of a P0155 Code?
The P0155 doesn't generate a lot of symptoms that you'll notice right away, but it all starts with the Check Engine Light. It's the first thing that will alert you to a problem with your engine and let you know it's time to start looking for other symptoms.
The other common symptom you'll notice is a failure on your emissions inspection. When an O2 sensor isn't working, especially before your catalytic converter, it won't pass your next inspection. There are strict rules about passing, so the wrong reading in the exhaust fumes can fail. You may also notice a reduction in performance in the engine when you accelerate.
There are also other symptoms you'll notice as time goes on, which can hurt your wallet. For example, the P0155 code can result in insufficient fuel economy because a lousy sensor will result in inefficient fuel usage. After all, the engine remains in an open loop. Another symptom you may notice is a rough engine idle as the engine struggles to maintain the proper air-to-fuel ratio.
The causes vary, but the most common issue is a defective oxygen sensor, specifically a problem with the heating element. Another cause can be wires that melt or a miscommunication with the PCM and O2 sensor. Issues with the PCM are rare, but they can fail. Other electrical problems like an open circuit, short to the ground near the sensor, or a blown fuse can cause your PCM to throw the P0155 code.
How Serious Is a P0155 Code?
When the Check Engine Light pops on, how serious could this be? If you use an OBD-II scanner to read the code and find a P0115, it's best to have the issue solved sooner rather than later. While it won't outright damage your engine immediately, it's a sign that your sensor can't reach the appropriate operating temperature or that there is an issue with your air-to-fuel mixture.
In any of these cases, you'll encounter problems with your engine if you ignore the code. You might damage the pistons, the catalytic converter, and other O2 sensors. Plus, the crankshaft and any valves will be under more pressure, and that can lead to failure if ignored.
How Easy Is It to Diagnose a P0155 Code?
Engine codes are simple to diagnose if you have the right equipment. To get started, all you need is an OBD-II scanner. The scanner can be connected to your engine’s DTC terminal access point, usually under the steering wheel. Once connected, you can scan the computer and pull any error codes. Once you confirm the P0115 code on your scanner, it's time to start looking for the source of the problem.
First, start by looking at the oxygen sensor. Take some time to study its appearance to see if it looks melted or damaged. Also, examine the wires to see if they're melted, frayed, or damaged in any way. Damage to these symptoms will result in problems with the sensor and can trigger a P0115 code.
Another electrical thing you can check is the fuse and relay for the O2 sensor. Use your owner's manual to identify the fuse and determine if it needs to be replaced. You can also use a multimeter to test the voltage through the circuit; if it has no voltage, it's not getting power. Make sure you check both the voltage and ground. The last thing to check is your engine’s PCM. While it's rare for an engine's computer to be the problem, it's worth checking on it just in case.
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