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P0155 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


A P0155 trouble code is defined as “02 Sensor Heater Circuit Malfunction in bank 2, sensor 1.


When the P0155 code is showing up on your OBD-II scanner, it indicates that the heater element of the oxygen sensor is taking a longer time than it normally should heat up. The power control module (PCM) will store the P0155 trouble code and the check engine light will come on to alert the driver of the problem.


There are several issues that can occur with a vehicle that can cause a P0155 trouble code to register on your OBD-II scanner. This can mean that the oxygen sensor (in bank 2, sensor 1) not working properly. This can also be due to the fact that there is a broken or bare wire leading to the oxygen sensor

This could signal that the fuse to the circuit for the oxygen sensor has blown. At times, this may mean that the engine coolant temperature sensor not working as it should normally. In other cases, this can mean that the power control module (PCM) is defective, though this is possible, this is far less likely to happen in comparison to the other causes. 


There are a few signs or symptoms that you should be on the lookout for that can be indicative of a P0155 trouble code.

  • The Check Engine Light will be illuminated. 
  • The vehicle will run rough. 
  • The vehicle may consume more fuel than usual. 
  • The vehicle can shut off on occasion. 
  • There may be a rotten egg smell coming from the exhaust
  • Black smoke rises out of the exhaust.

If you notice that any of these problems are occurring with your vehicle, it may be a visible sign that you have a P0155 trouble code. 


Mechanics should follow this process for diagnosing and confirming a P0155 trouble code: 

  • Use an OBD-II scanner to collect the trouble codes that have been stored by the power control module (PCM).
  • Look for breaks and bareness in the wiring that leads to the oxygen sensors.
  • Use the OBD-II scanner to view live data to confirm the oxygen sensor is working appropriately.
  • If the coolant temperature sensor is not operating properly, the PCM will store this code also. That means you should inspect and test this as well.
  • In rare cases, the power control module (PCM) may be defective. In this case, it would require an advanced diagnosis to determine whether this is the problem. This should be considered last, only after every other possible attempt at repair has been exhausted.

Following this step-by-step diagnosis is going to be the best way to confirm this trouble code. It is also going to be the safest and most effective way to avoid any of the most common mistakes, listed below. 

Common mistakes

When mechanics are confirming this trouble code and working to fix it, it isn’t uncommon that they will replace the oxygen sensor before inspecting the other components. This can lead to replacing a perfectly good, functioning oxygen sensor. Another one of the most common mistakes in properly diagnosing and fixing this code is not inspecting the wires leading to the oxygen sensor. You should be checking for breaks in wiring and/or bare wires before the oxygen sensor is replaced. 

How serious is this?

The P0155 trouble code is considered to be a moderately serious code. The reason that it is treated as such is that this code negatively affects the drivability of the vehicle. It also leads to poor fuel consumption and fuel economy when this trouble code is present.

What repairs can fix the code?

There are a few common repairs that can quickly and easily fix this trouble code:

  • Make sure to fix broken wires or bare wires, if any are present. 
  • Replace the coolant temperature sensor
  • Replace the oxygen sensor
  • In rare cases, you may need to replace the power control module (PCM).

Related codes

None listed.


Though a P0155 trouble code is not detrimental to the vehicle, it can have a negative impact on the fuel economy and the performance of the vehicle. It is advised that you you confirm this code and have it fixed as soon as you notice any of the symptoms associated with a P0155 trouble code. 

P0155 Code – What Does It Mean & How To Fix It