What Codes Will This Page Cover?
- P0155 O2 Sensor Heater Circuit – Bank 2 Sensor 1
- P0161 O2 Sensor Heater Circuit – Bank 2 Sensor 2
- P0167 O2 Sensor Heater Circuit – Bank 2 Sensor 3
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What Is the P0155 Code?
Symptoms
Causes
Seriousness
Can I Still Drive?
Diagnose
Difficulty of Inspecting
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The P0155 code relates to the heated oxygen sensors that your vehicle relies on to get your engine to operating temperature quickly so as not to stay in open-loop operation too long. The P0155 code occurs when the Power Control Module (PCM) tests the upstream heated oxygen sensor’s circuit on Bank 2, or one side of a V-configured engine like a V6 or a V8, and detects a short in the circuit or too much resistance in the heater circuit. The codes P0161 and P0167 relate to the other two sensors located on the Bank 2 side of the engine and exhaust system.
As we mentioned, the PCM performs tests on the heated oxygen sensors to prevent your engine from operating in open-loop mode for too long. Open-loop mode is found in fuel-injected motors, which makes up the majority of all motors today, and means that the engine is operating independently of any oxygen or air-to-fuel sensors and makes no adjustments to that mixture. The heated oxygen sensors are needed to ensure that the engine can have a reliable sensor to listen to and start adjusting the air and fuel ratio accordingly. This then lands the motor in closed-loop mode. Nevertheless, there are many cases when a particular sensor isn’t working that the ECM will infer a signal in order to keep the vehicle operational. This would then store a substituted value in the freeze frame data that wouldn’t change and could be picked up with a scanner later.
More About The P0155 And Related Codes
The P0155 code appears when the PCM performs a circuit test on the front end of the Bank 2 system and runs into any circuit issues or excessive resistance problems with the oxygen sensor. What this means is that it will take longer for the motor to enter the closed-loop mode. As the O2 heater reaches operating temperature, the oxygen sensor responds by adjusting according to the oxygen content of the exhaust surrounding the sensor. The PCM tracks how long this time takes for the oxygen sensor to begin switching, and if it determines that it is taking too long, it will trigger the P0155 code.
Another thing to note with the P0155 code is that this time measurement performed by the PCM begins after the engine coolant temperature sensor indicates that the engine has warmed up to sufficient temperature. If this signal lingers or is below a set lean-to-rich cross-count point, which is usually around 450 millivolts, the P0155 code will trigger. This is also the case with the P0161 and P0167 codes as these other oxygen sensors are also needed for this system check to be completed properly.
What Are the Symptoms of a P0155 Code?
One of the very first and noticeable symptoms of a P1055 code is that the Check Engine Light will illuminate and stay on. In a lot of cases, there are no abnormal or physical symptoms that immediately appear, however, the code can cause the motor to run rich and possibly fail an emissions test. This is because the Nitric Oxide (NOx) levels will have become elevated due to the richer nature of the engine running in open-loop mode. Nitric Oxide is formed during the combustion process when there are lower fuel levels causing a lean air-to-fuel ratio. Combustion temperatures increase during a lean condition because there is more oxygen content and not enough fuel to burn. Another symptom to look out for is decreased fuel economy and a rougher idling motor when the vehicle is stopped. The decreased fuel economy will take a little longer to notice but will be noticeable once you have to start filling up your car with gas more frequently. The rough idle is usually a result of the failure of the engine to adjust to the proper air to fuel ratio needed to operate efficiently.
What Are Some Causes of a P0155 Code?
Some of the most common causes of a P0155 code relate to faulty or broken pre-catalyst oxygen sensors. A defective oxygen sensor won’t be able to relay the proper temperature and oxygen readings needed for the PCM to adjust the proper air to fuel mix ratios and will cause the P0155 code to appear. Another common cause of the error code is poor or faulty wiring or wiring harnesses around the oxygen sensor. You could also have an open circuit or short to the ground around the oxygen sensor and this will often prevent the sensor from operating properly.
Another common cause of the P0155 code relates to the engine coolant temperature sensor and its operating abilities. As we mentioned, the engine coolant sensor is vital in the PCM’s role of monitoring the engine operating temperature, and in turn, switching the engine to the normal closed-loop operating mode. If the coolant sensor is unable to relay the proper engine coolant temperature, this will disrupt this process and trigger the PCM to throw out the P0155 code. This also applies to codes P0161 and P0167 codes as these oxygen sensors perform similar roles and all need to work in unison for the PCM to complete the engine temperature test. Finally, a faulty PCM can be a cause of the code setting if the module is unable to perform this common system check.
How Serious Is the P0155 Code?
The P0155 code would be considered a moderate to severe OBD code because it has the capability of turning into much costlier problems for your engine. The code by itself does not present immediate issues, but it is a strong indicator that your engine is incapable of reaching a proper operating temperature. Because the issue inherently relates to the operating temperature of the engine, this isn’t’ something that you should forego having a qualified technician check out. This is because operating your vehicle when it hasn’t set to closed-loop mode can force your car to over-exert itself and this can put additional strains on parts like your valves, pistons, and camshafts. You shouldn’t risk further damage to your motor so whenever you see the P0155 code, take your vehicle immediately to a qualified technician to properly diagnose and repair the issues.
Can I Still Drive with a P0155 Code?
While there are no immediate physical symptoms that you may notice with the P0155 or its related codes P0161 and P0167, it’s still not recommended to drive your vehicle when these codes appear. This is because you are risking further damage to your vehicle by operating the car while it is still in open-loop mode and not receiving the proper air to fuel mixture ratio. This is why we recommend that you immediately take your vehicle to a qualified technician once the P0155 code appears so that they can properly inspect it.
How Easy Is It to Diagnose a P0155 Code?
Since the P0155 and its related codes deal with the operating capabilities of the heated oxygen sensor, it is relatively straightforward to diagnose the issue. Even with it being a straightforward process, we recommend that you leave this to qualified technicians that have prior experience diagnosing these sorts of issues.
The first step needed in diagnosing the P0155, as well as the P0161 and P0167 code, is to reset the code and perform a quick driving test. If the Check Engine Light remains illuminated then you will want to make sure that the oxygen sensor is receiving the right battery voltage by using a multimeter. You will also want to disconnect and reconnect the wiring harness for the Bank 2 and appropriate sensor. For codes P0161 and P0167 you will be looking at the Sensor 2 and Sensor 3, respectively. If you find damage to the wiring harness or electrical terminals, these will need to be replaced. However, if they’re not, then you will proceed to check the engine ground and look for any loose connections or corrosion. You can find more information on battery and terminal repair guides here. This will need to be removed or replaced before restarting the diagnostic process.
How Difficult Is It to Inspect a P0155 Code?
As we mentioned, the diagnosis process for a P0155 code can be relatively straightforward, it should still be left to a qualified technician. This applies to the inspection and repairing process as well, as you want to make sure that you are repairing or replacing the right part. Even removing the oxygen sensor can be difficult if you don’t have an oxygen sensor set or the proper scanner equipment to test the operability of the sensor. Sometimes, even a heating element is needed to remove the sensor located near the exhaust. This is why this sort of work is best delegated to qualified technicians with the proper tools and expertise to perform these repairs, and not try and DIY these repairs yourself.
Need Additional Help with Your P0155 Code?
Ultimately, we have learned that the P0155 and its related codes can become a severe issue if they are not attended to in a timely manner. To get your car back to its full operating capabilities, contact a service center near you and have your vehicle inspected and back on the road immediately.
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