P0155Powertrain
Powertrain · SAE
O2 Sensor Bank 2 Sensor 1 – Heater Circuit Fault
Meaning
The heater element inside the upstream lambda sensor on Bank 2 has an electrical fault — open circuit, short circuit, or resistance outside the permitted range. The sensor may not reach operating temperature quickly enough, impairing mixture control during the engine warm-up phase.
Common causes
- Internal heater element broken or short-circuited (sensor failure)
- Interrupted heater supply circuit (fuse, relay, upstream wiring)
- Heater supply wire short to ground or to supply
- Corroded sensor connector with high contact resistance
- Failed heater driver inside the ECU
Symptoms
- MIL (Check Engine) warning light on
- Extended open-loop phase after cold start
- Possible increased fuel consumption during warm-up
- Elevated emissions during start-up transient phase
- Possible companion mixture fault codes on Bank 2 (P0150/P0151/P0152) if sensor remains cold
Severity
Moderata: The sensor may still function at fully warm engine temperature via convective heating, but the warm-up phase is compromised and emissions are elevated in that window.
What to do
- Measure the heater element resistance of sensor B2S1 with the sensor cold (typically 2–30 Ω per manufacturer specification); out of range indicates internal failure.
- Check heater supply voltage at the sensor connector with the engine running; should be close to battery voltage.
- Check continuity and insulation of the heater ground wire.
- Check the condition of the fuse and relay supplying the O2 sensor heater circuit.
- Replace the upstream O2 sensor B2S1 if heater resistance is out of range or shorted; repair wiring if the fault is in the external circuit.