OBD-II code · Powertrain (generic, extended)
P2256 O2 Sensor Heater Control Circuit Low Bank 1 Sensor 2
The ECU detects a low-side voltage below threshold on the heater control of the rear oxygen sensor on bank 1. The heater driver may be stuck on or shorted to ground.
Is it safe to drive with P2256?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyHeater wire shorted to ground
- PossibleInternal heater short
- Less likelyConnector pins corroded - high contact resistance
Symptoms
- Check engine light on after several drive cycles
- Slightly increased fuel consumption during cold start
- Delayed entry into closed-loop fuel control
- Failed emissions inspection (lambda readiness)
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.5–1.5 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Oxygen Sensor, Oxygen Sensor Heater Circuit
Related codes
- P2253O2 Sensor Negative Current Control Circuit High (Bank 1 Sensor 1)
- P2254O2 Sensor Negative Current Control Circuit Low (Bank 2 Sensor 1)
- P2255O2 Sensor Negative Current Control Circuit High (Bank 2 Sensor 1)
- P2257Secondary Air Injection System Control A Circuit Low
- P2258Secondary Air Injection System Control A Circuit High
- P2259Secondary Air Injection System Control B Circuit Low
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.