Powertrain, generic (extended)

P256F A/C Request B Circuit Range/Performance

Check engine lightUsually off
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Climate control logic sends inconsistent B request
Intermittent connection on the B request line
Fault in a second evaporator or compressor stage control

Symptoms

  • Rear or second-stage cooling unreliable
  • Idle dips or surges with A/C operation

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€40–450
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

ac request input bhvac module

Related codes

P2522P2523P2524P255F

References: law.cornell.edu, saabwisonline.com.