Lexus: What Does Error Code P0155 Mean?

P0155 is the OBD-II generic code indicating that the PCM has detected a problem with the bank 2 oxygen sensor 1.

By Pouria Savadkouei - October 17, 2018

This article applies to the Lexus IS, RX, GS, LS, and ES (2005-Present).

Every Lexus vehicle comes equipped with an OBD connector which can be used to send messages to an OBD2 troubleshooting reader like the one below. Simply connect the scanning tool (or a computer with scanning software downloaded) to the connector (located under the steering wheel) and the readout will show you Diagnostic Trouble Codes that might be affecting your car. From there, you can look up the code at to learn what's going on and try to repair it yourself. If you are not comfortable diagnosing and repairing your car, please take it to a Lexus service center. Scanner programs and tools vary in price. An app can be purchased for $4.95, and an OBD-II Scanner/Code Reader can be purchased for anywhere between $19 and $300+ depending on what service functions you need.

P0155 Definition

P0155 is the OBD-II generic code indicating that the PCM has detected a circuit malfunction with the bank 2 oxygen sensor 1.

P0155 Explained

The O2 Sensor unit is located just in front of the catalytic converter and its job is to examine the concentration of oxygen in the exhaust gas coming out of the engine. The PCM (powertrain control module) uses this information to adjust the amount of air that mixed into the fuel (air/fuel ratio) going into the motor. Nowadays, most cars are equipped with heated O2 sensors (HO2S) which also contain a heater to bring the unit to operating temperature, which in turn, allows the PCM to receive the correct data soon after the car is turned on. When the PCM detects an issue with the heated O2 Sensor, the check engine light will turn on.

P0155 refers to such an issue specifically in sensor 1 of bank 2. Bank 1 is on the side of the engine that has the #1 cylinder. Bank 2 is the opposite side of the engine. If you have a four-cylinder, there will only be one bank, and you would not get this code.

P0155 Symptoms

  • Poor fuel economy (not noticeable)
  • Failed emissions test
The only symptom that is actually noticeable is the check engine light coming on.

P0155 Common Causes

  • A problem on the ground side of the O2 sensor heater circuit
  • A problem on the power side of the O2 sensor heater circuit
  • O2 sensor heater element has high resistance
  • O2 sensor heater element has an open circuit

P0155 Diagnosis and Repair

The number one most common repair for this problem is replacing the O2 Sensor itself. However, if the problem is caused by circuit wiring, the repair would be to replace the wiring or connection for Bank 2, Sensor 1, either for ground or for power.

  • Consult your vehicle's wiring diagram to determine the pins for ground and power on the connector
  • Test the ground side of the circuit, and/or
  • Test the power side of the circuit
If the issue is not from the wiring,

  • Test the heating element

Final Notes

Although it is ok to drive the car with this issue, it does cause decreased fuel-efficiency and will cause the car to fail emissions tests. So, while it is not a critical problem, it is beneficial to get it fixed early.
Once all repairs have been taken care of, erase the code from the car's ECU. Then proceed to drive it for several miles to make sure the code does not come back and the issue is resolved.

Code P0135 is the exact same code but for the opposite side bank (bank 1).

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