P0056Powertrain
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. This sensor monitors bank 2 catalytic converter efficiency; a heater fault compromises this diagnostic function.
Common causes
- Broken internal heater element in the O2 sensor B2S2
- Open or corroded wiring/connector on the bank 2 heater supply line
- Blown O2 heater fuse
- Short to ground in the heater wiring
- Faulty heater relay
Symptoms
- Check engine light (MIL) on
- Possible related catalyst efficiency code for bank 2 (P0430)
- No drivability symptoms in most cases
- Bank 2 emissions monitoring compromised
Severity
Low to moderate: no direct drivability impact, but bank 2 catalyst monitoring is impaired.
What to do
- Measure heater resistance at connector pins (typical 4–30 Ω; open = replace sensor)
- Check 12 V supply and ground at B2S2 connector with ignition ON
- Inspect wiring to ECU for damage or corrosion
- Check the O2 heater fuse
- Replace O2 sensor B2S2 if external circuit is intact