OBD-II code · Powertrain (generic, extended)
P256F A/C Request B Circuit Range/Performance
A/C request input B is electrically intact but its value does not match the system context — same failure mode as the input A performance fault, applied to the second HVAC channel.
Is it safe to drive with P256F?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyHVAC module sending inconsistent request B
- Less likelySensor element aged beyond calibration window
- Less likelySensor mounting loose - signal damping
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.4–2 h
- Emissions test
- Usually unaffected
- Parts involved
- AC Request Input B
Related codes
- P2522A/C Request B Circuit
- P255FA/C Request A Circuit Range/Performance
- P256CEngine Idle Speed Selector Sensor/Switch Circuit Low
- P256DEngine Idle Speed Selector Sensor/Switch Circuit High
- P256EEngine Idle Speed Selector Sensor/Switch Circuit Intermittent/Erratic
- P2570Direct Ozone Reduction Catalyst Temperature Sensor Circuit High
- P2571Direct Ozone Reduction Catalyst Temperature Sensor Circuit Intermittent/Erratic
- P2572Direct Ozone Reduction Catalyst Deterioration Sensor Circuit
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.