P0155: O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1)
The heater inside the oxygen sensor isn't working. The heater gets the sensor working quickly after a cold start. This is the upstream (before the catalytic converter) sensor on bank 2. The upstream sensor controls fuel mixture, so a bad one can hurt fuel economy.
Green, yellow, red: three ways P0155 can look
The same code can be a quick fix or a reason to pull over. Match your situation to the closest example.
Keep an eye on it
Light on, car drives normally. Safe to drive and schedule the repair.
Schedule a repair
Fuel economy dropping, or you need to pass inspection. Replace the sensor or fix the wiring soon.
Stop and get help
The sensor code is with misfire codes or a flashing light. Deal with the misfire first and stop driving soon.
Symptoms you might notice
- Check engine light
- Poor fuel economy
- Failed emissions test
Common causes, cheapest first
- Failed oxygen sensor heater (most common; the sensor is replaced)
- Blown fuse for the O2 heaters
- Damaged wiring near the exhaust
What you can check before calling
- Look for exhaust leaks or soot near the sensor
- Check that the sensor connector is attached and not melted
A code points to a system, not a part. Replacing parts based on the code alone is how people spend money without fixing the problem. Testing confirms the cause first.
Generic codes (second character 0) mean the same thing on every vehicle. Some manufacturers add their own details, so check service information for your exact vehicle.
More oxygen sensors codes
- P0130
O2 Sensor Circuit Malfunction (Bank 1, Sensor 1) - P0131
O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1) - P0132
O2 Sensor Circuit High Voltage (Bank 1, Sensor 1) - P0133
O2 Sensor Circuit Slow Response (Bank 1, Sensor 1) - P0134
O2 Sensor Circuit No Activity Detected (Bank 1, Sensor 1) - P0135
O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
Look up another code
Cummins fault code (like 1922), J1939 SPN and FMI (like SPN 3251 FMI 0), or an OBD-II code (like P0420).
Questions
What does P0155 mean?
P0155 means "O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1)". The heater inside the oxygen sensor isn't working. The heater gets the sensor working quickly after a cold start. This is the upstream (before the catalytic converter) sensor on bank 2. The upstream sensor controls fuel mixture, so a bad one can hurt fuel economy.
Can I drive with code P0155?
It depends on what the vehicle is doing. Green: Light on, car drives normally. Safe to drive and schedule the repair. Yellow: Fuel economy dropping, or you need to pass inspection. Replace the sensor or fix the wiring soon. Red: The sensor code is with misfire codes or a flashing light. Deal with the misfire first and stop driving soon.
What causes P0155?
The most common causes are: failed oxygen sensor heater (most common; the sensor is replaced); blown fuse for the O2 heaters; damaged wiring near the exhaust.
Is P0155 a serious code?
It can be. The sensor code is with misfire codes or a flashing light. Deal with the misfire first and stop driving soon.
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