P0051HO2S Heater Control Circuit Low (Bank 2 Sensor 1)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The heated oxygen sensor on bank 2 is the upstream sensor (sensor 1, before the catalytic converter), used for mixture control. Its heating element brings it quickly to operating temperature. Typically the heater receives battery voltage via a fuse, and the engine control module switches the ground side with a pulsed signal while checking that the circuit state matches the command. P0051 means the control module measures too low a voltage or current in the heater control circuit, for example because of a short to ground or, depending on the system, a burnt-out element. Which physical fault sets the general, low or high code is defined by each manufacturer. Without heating, closed-loop mixture control starts late and cold-start emissions rise. Bank 2 codes occur only on engines with two exhaust banks (V or boxer engines).
- What you may notice
- Check engine light on
- Usually no noticeable drivability problem
- Closed-loop control starts late after a cold start
- Emissions test or readiness check failed
- Likely causes
- LikelyControl wire shorted to ground, or heating element burnt out (system-dependent)
- PossibleSupply interrupted or fuse blown
- PossibleCorroded connector with high contact resistance
- RareOutput driver or software of the engine control module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €80 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.