P0161Powertrain
Powertrain · SAE
O2 Sensor Heater Circuit — Bank 2, Sensor 2
Meaning
The ECU detected an electrical fault in the heater circuit of the downstream (post-catalyst) oxygen sensor on bank 2. The fault prevents the sensor from reaching operating temperature quickly, compromising bank 2 catalyst efficiency monitoring.
Common causes
- Broken internal heater element in the O2 sensor B2S2
- Open or corroded/damaged wiring or connector
- Blown O2 heater fuse
- Short to ground in the heater wiring
- Faulty heater relay
Symptoms
- Check engine light (MIL) on
- Possible appearance of P0430 (bank 2 catalyst efficiency)
- No drivability symptoms in most cases
- Bank 2 emissions monitoring compromised
Severity
Low to moderate: no direct drivability impact, but bank 2 catalyst monitoring function is impaired.
What to do
- Measure heater resistance at B2S2 connector pins (typical 4–30 Ω; open = replace sensor)
- Check 12 V supply and ground at connector with ignition ON
- Inspect wiring from sensor to ECU for breaks or corrosion
- Check the O2 heater fuse
- Replace O2 sensor B2S2 if wiring is intact