P0645A/C Clutch Relay Control Circuit
- Generic OBD-II code · Powertrain
- How the car detects it
- The engine module switches the A/C compressor clutch relay through a low-side driver once the climate control requests cooling. P0645 is the general circuit fault of the relay coil control, usually an open circuit. GM Europe's 2011 Saab 9-5 sets P0645/P0646 for an open or short to ground and P0647 for a short to voltage, with the engine running and A/C requested; Ford's commercial trucks report it without the check engine light. Older Saab diesels (Bosch EDC16/PSG16) use a different assignment (P0645 short to voltage, 0.6 s). GM found a no-start with P0645 on the 2002–04 Alero/Grand Am 3.4 L because a shorted compressor clutch coil blew a fuse shared with the engine control; Ford traced warm air with P0645 on the 2020–23 Explorer to spread terminals at the body module. The compressor then does not engage or runs constantly.
- What you may notice
- A/C not cooling (compressor does not engage)
- Compressor runs constantly
- Check engine light usually off, code stored only
- Rarely no start if a shared fuse has blown (GM 3.4 L)
- Likely causes
- LikelyA/C clutch relay faulty (coil open)
- LikelyControl wire or connector open, terminals spread
- PossibleRelay or clutch supply fuse blown (e.g. shorted clutch coil)
- RareOutput driver in the module faulty
- Repair
- Easy · Often possible to do yourself.Typical cost: €15 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.