P0036Powertrain
Powertrain · SAE
O2 Sensor Heater Circuit — Bank 1, Sensor 2
Meaning
The ECU detected an electrical fault in the heater circuit of the downstream (post-catalyst) oxygen sensor on bank 1. Sensor 2 is used to monitor catalytic converter efficiency; a heater fault impairs this diagnostic function and may mask catalyst degradation.
Common causes
- Broken internal heater element in the O2 sensor B1S2
- Open or corroded wiring/connector on the 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 (P0420)
- No drivability symptoms in most cases
- Emissions monitoring compromised
Severity
Low to moderate: no direct drivability impact, but catalyst monitoring is impaired, risking undetected catalyst deterioration.
What to do
- Measure heater resistance at connector pins (typical 4–30 Ω; open circuit = replace sensor)
- Check 12 V supply and ground at the heater connector with ignition ON
- Inspect wiring from B1S2 to ECU for damage or corrosion
- Check the O2 heater fuse
- Replace O2 sensor B1S2 if external circuit is intact