OBD-II code · Powertrain (generic)
P0155 O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1)
Same condition as P0135 but on the upstream sensor of bank 2. The sensor heater warms the element to operating temperature (~600 °C); without it the lambda sensor stays inactive in closed loop and the ECM cannot trim mixture.
Is it safe to drive with P0155?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyHeater element open-circuit
Symptoms
- Check engine light on after several drive cycles
- Slightly increased fuel consumption during cold start
- Delayed entry into closed-loop fuel control
- Failed emissions inspection (lambda readiness)
Repair at a glance
- Difficulty
- Easy
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.3–1.5 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Oxygen Sensor Upstream, Oxygen Sensor Heater Relay
Related codes
- P0135O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
- P0141O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)
- P0161O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 2)
- P0152O2 Sensor Circuit High Voltage (Bank 2, Sensor 1)
- P0153O2 Sensor Circuit High Voltage (Bank 2 Sensor 1)
- P0154O2 Sensor Circuit No Activity / Slow Response (Bank 2 Sensor 1)
- P0156O2 Sensor Circuit Malfunction (Bank 2, Sensor 2)
- P0157O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)
- P0158O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.