P256FA/C Request B Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P256F is the plausibility fault of a second A/C request input, B. Its wiring checks out, yet the engine module finds the state or timing illogical, for instance a request present while the first input and the climate controller say no cooling is wanted, or one that flickers instead of holding steady. Why a vehicle has two request inputs is up to each maker; a rear evaporator, a second compressor stage or a redundant cross-check line are plausible reasons. No maker documents P256F publicly. The legal basis is CARB's A/C component monitoring, which also covers A/C parts used as inputs to other diagnostics. Networked designs like the 2011 Saab 9-5, which take the request over the data bus, report trouble as communication codes instead. P2522 is the general fault on B, P255F the matching test on A.
- What you may notice
- Rear or second-stage cooling unreliable
- Idle dips or surges with A/C operation
- Likely causes
- PossibleClimate control logic sends inconsistent B request
- PossibleIntermittent connection on the B request line
- RareFault in a second evaporator or compressor stage control
- Inspection (ITP)
- Can matter for the ITP: it concerns the emissions system.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €40 – €450
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.