Powertrain, generic (extended)

P2520 A/C Request A Circuit Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P2520 is set when the voltage on A/C request input A stays below the band the engine module accepts. Depending on whether the input is active-high or active-low, a grounded wire then reads as a permanent request or as none at all – either way the module distrusts it. Most often a harness rubbed through to body metal, a pinched wire behind the dashboard or a climate panel output stuck low is behind it. No maker publishes P2520 with thresholds; CARB only requires that A/C parts influencing fuel or spark control be checked, and on many cars with a networked request such as the 2011 Saab 9-5 the wired input does not exist. Unlike P2519 the circuit is not simply open, and P2521 is its high counterpart. The A/C may refuse to run or run unasked.

Likely causes

Request wire shorted to ground
Climate control output stuck low
Engine module input stage faulty

Symptoms

  • A/C does not switch on, or compressor runs although A/C is off
  • Idle speed behaves oddly when the A/C is toggled

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€40–400
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

P2519P2521P2523

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