Powertrain, generic (extended)

P255F A/C Request A Circuit Range/Performance

Check engine lightUsually off
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P255F flags the A/C request A input as electrically sound but implausible: the request may switch on and off far more often than a real compressor demand would, stay set while the climate control is off, or disagree with what the engine module sees from the compressor side. The request lets the engine prepare for the compressor load by raising idle speed and torque reserve. CARB section (e)(12) requires monitoring of electronic A/C components when switching the A/C alters fuel or spark control, including failures that trigger the alternate strategy with the A/C off, phased in over 2006 to 2008. Saab's 2011 9-5 is an example of a design without such a wire, receiving the request as a bus message. No maker documents P255F publicly. P2519 is the general fault on input A, P256F the same check on input B.

Likely causes

Climate control module sends erratic requests
Loose contact on the request line causing chatter
Refrigerant pressure switch cycling abnormally

Symptoms

  • Idle speed fluctuates when the A/C cycles
  • A/C cooling intermittent or switched off

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 ahvac module

Related codes

P2519P2520P2521P256FP0645

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