P0645: A/C clutch-relay command disagrees with circuit feedback

P0645 in the cited 2010 GM table concerns the air-conditioning clutch-relay control circuit. The ECM detects disagreement between the commanded driver state and the actual control-circuit state. This is an electrical consistency check, not a direct test of cooling output.

A requested clutch is not a verified clutch circuit

A scan tool can show that the controller requested operation while the circuit fails to follow. Conversely, a visible compressor symptom does not identify the relay-control path as its cause. The code narrows the investigation to the monitored electrical relationship, but does not isolate the relay, wiring or driver.

The summary does not provide a connector pinout, coil-resistance specification or a safe jumper method. Those belong to the matching vehicle service information.

Reproduce the enabled operating state

The documented check requires the engine to be running above its minimum speed and run/crank voltage within the specified range. It then counts twenty failing samples out of twenty-five at quarter-second intervals. A key-on inspection with the engine stopped does not exercise that same monitor.

Record the relay command, the available feedback and supply condition together. This is a practical inference from the command-versus-state design: without both states, a snapshot cannot explain the disagreement.

After a demonstrated circuit defect is repaired, confirm that the monitor evaluates successfully. A cold vent temperature alone does not establish that the relay-control diagnostic has passed or that an intermittent electrical fault is gone.

Application limits

Document-level 2010 GM diagnostic table; per-code vehicle/engine/calibration applicability not established.

Source

10OBDG13 Engine Diagnostics, physical PDF pages 78.