P0056
HO2S Heater Control Circuit (Bank 2 Sensor 2)
The PCM found an electrical problem in the heater circuit for the rear oxygen sensor on bank 2. That heater helps the post-catalyst sensor warm up quickly so the catalyst monitor can run correctly. When the circuit fails, the light comes on and emissions monitoring becomes less reliable.
- SEV
- 3/5
- DRIVE
- CAUTION
- DIY
- $20-$160
- SHOP
- $120-$450
01 / Definition
P0056 means the PCM detected a heater control-circuit fault for Bank 2 Sensor 2, the downstream oxygen sensor after the catalytic converter on the bank opposite cylinder 1. Common causes include an open heater element, wiring damage, blown fuse, poor ground, or a control-side fault. The code is electrical in nature and should not be confused with a converter-efficiency code.
02 / Drive status
With caution. The car usually remains drivable, but the rear O2 monitor and emissions readiness may be affected. It should still be repaired soon so the check engine light does not hide other converter or sensor faults.
03 / Symptoms
- Check engine light on
- Failed emissions test
- Oxygen-sensor monitor not ready
- Reduced catalyst-monitoring accuracy
- Usually no major drivability symptoms
04 / Causes
| 1 | Failed heater element inside the Bank 2 Sensor 2 oxygen sensor | high |
|---|---|---|
| 2 | Damaged, melted, or corroded wiring or connector at the rear O2 sensor | high |
| 3 | Blown fuse or failed relay feeding the heater circuit | medium |
| 4 | Poor ground or open circuit in the heater power supply | medium |
| 5 | PCM driver fault | low |
05 / Diagnostic sequence
- 01Verify P0056 and scan for related Bank 2 rear O2 and heater codes.
- 02Inspect the Bank 2 Sensor 2 wiring and connector for exhaust-heat damage, water intrusion, or loose terminals.
- 03Check the heater fuse and relay if the vehicle uses a dedicated heater feed.
- 04Measure heater resistance and compare it with factory specification.
- 05Verify power and ground at the heater circuit while following the service-manual test procedure.
- 06Repair harness faults and confirm the heater monitor can run after clearing codes.
- 07Replace the sensor if the heater element is out of specification and the rest of the circuit checks good.
06 / Repairs
| 1 | Repair damaged wiring, connector pins, or terminals at Bank 2 Sensor 2 | $20-$150 |
|---|---|---|
| 2 | Replace a failed fuse or relay supplying the rear O2 heater circuit | $10-$80 |
| 3 | Replace the Bank 2 Sensor 2 oxygen sensor if the heater element has failed | $60-$240 |
| 4 | Diagnose PCM driver faults only after the sensor and external circuit test correctly | $150-$600 |
07 / Related codes
08 / FAQ
What does Bank 2 Sensor 2 mean?
It is the oxygen sensor after the catalytic converter on the side of the engine that does not contain cylinder 1.
Is P0056 a catalytic-converter failure code?
No. It is an electrical heater-circuit code for the rear oxygen sensor.
Can P0056 cause a failed emissions test?
Yes. The check engine light and incomplete rear O2 monitoring can both cause emissions-test failure.