Powertrain, generic · Computer and auxiliary outputs

P0647 A/C Clutch Relay Control Circuit High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

The engine module switches the A/C compressor clutch relay through a low-side driver once the climate control requests cooling. P0647 means the voltage at the control output stays too high while the driver switches on (it should pull to ground) – the control wire is shorted to voltage; the driver shuts off for protection and the relay does not pull in, so there is no cooling. GM Europe's 2011 Saab 9-5 uses P0647 only for a short to voltage (check: less than 0.3 V on the control wire with ignition on and the module unplugged); Saab's EDC16 diesels use it for an open circuit instead (0.6 s). Not emission relevant; usually stored without the check engine light.

Likely causes

Control wire shorted to a supply wire (chafing)
Relay with internal short (coil bypassed, very low resistance)
Wrong relay fitted
Output driver in the module faulty

Symptoms

  • A/C not cooling
  • Compressor clutch never engages
  • Code stored, check engine light usually off

Repair estimate

DifficultyEasyDIY possible
Parts and labour€15–250
Time0.3–1.5 h

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

Parts involved

ac clutch relayrelay control circuitengine control module

Related codes

P0645P0646P0530P0534

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