P0645
A and C Clutch Relay Control Circuit
A general circuit fault on the A/C clutch relay control - the line over which the ECU engages the magnetic clutch to drive the A/C compressor.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: easy
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
Common causes
Ordered by how often each turns out to be the cause.
- Open in relay or wiringCommon
Parts involved
- AC Clutch Relay
P0645 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.