P0155 – Meaning, Causes, Symptoms, & Fixes

Code P0155 Definition

O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)

Code P0155 Meaning

Heated oxygen sensors contain heating elements to help them get to operating temperature quickly in order to minimize the amount of time spent in open loop operation (A fixed rich mixture). Code P0155 occurs when the powertrain control module tests the upstream heated oxygen sensor’s heater circuit on Bank 2 and detects a short in the circuit or excessive resistance in the heater circuit.

P0155 Symptoms

  • Check Engine Light is on
  • The engine may be running rough
  • Decreased fuel economy
  • Rough running engine

P0155 Causes

  • Faulty rear most oxygen sensor
  • Faulty wiring/connections
  • Short or open ground in the wiring
  • Engine coolant temperature sensor is not operating correctly
  • Faulty Power Control Module

Code P0155 Severity – Moderate    

This Diagnostic Trouble Code (DTC) does not need to be attended to immediately, but this DTC could result in more costly repairs in the future.

Code P0155 Common Diagnosis Mistakes

Replacing the oxygen sensor when the issues could actually lie in the catalytic converter, wiring/connections, or an exhaust leak before the oxygen sensor.

Code P0155 Diagnosis Steps

  • Tools Needed to Diagnose:

How To Diagnose P0155

This video does a great job of outlining the diagnostic process for P0155, but we have provided an overview below:

  1. Do a road test. Clear the fault codes with your FIXD sensor and drive around to verify a failure.
    1. If the Check Engine Light comes back on continue to Step 2
  2. Check that the O2 sensor is getting battery voltage by using your multimeter.
    1. Consult your vehicle repair manual to locate the harness connector for the O2 sensor
    2. Disconnect the harness connector and turn the ignition to the on position (do not crank car)
    3. Test O2 sensor for proper voltage with a multimeter using the instructions from your vehicle’s repair manual.
  3. Visually check the electrical connections, wire harness, and metal tabs in terminals for any damages
    1. Damages found? Replace O2 Sensor – Clear code
    2. No damage? Continue on to Step 4
  4. Check the engine ground – Consult your repair manual to find where the engine ground is located
    1. Corrosion? Loose connections? Remove corrosion/tighten and restart the diagnostic process


* Still having trouble finding the issue with your vehicle? Please take it to the nearest auto shop so that they may check other possible issues including the Engine Control Module (ECM).

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Comments 4


April 27, 2018

What about u1501 code?

Mason Mayes

April 27, 2018

Hi James! We really appreciate you reaching out! “U” indicates it is a network code. However, when codes start with U1XXX, it indicates they are reserved for manufacturer specific codes which we do not have access to at this time. A manufacturer specific scan tool is required to diagnose these types of codes.


March 23, 2019

When the repair refers to a “bank,” what is that telling me?


April 29, 2019

Patrick “bank” is referring to one side or the other of the engine bank one 1 would be left side of engine bank 2 is right side of engine thats looking at the engine while in the driver seat so from the front of the car it would be opposite hope that helps.

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