Diagnostic Aids

For HVAC system concerns, refer to HVAC Preliminary Checks in Heating, Ventilation, and Air Conditioning.
If condition is intermittent refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

DTC P0645

Step	Action	Yes	No
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views
1	IMPORTANT: This diagnostic trouble code (DTC) will only set for a failure on the control side of the A/C clutch relay. Did you perform the Diagnostic System Check - HVAC Systems - Manual?	Go to Step 2	Go to Diagnostic System Check - HVAC Systems - Manual
2	Turn ON the ignition, with the engine OFF. Command the A/C Relay ON and OFF with a scan tool. Does the A/C Relay turn ON and OFF with each command?	Go to Step 3	Go to Step 4
3	Observe the Freeze Frame/Failure Records for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition?	Go to Step 4	Go to Diagnostic Aids
4	Turn OFF the ignition. Disconnect the A/C clutch relay. Turn ON the ignition, with the engine OFF. Probe the ignition 1 voltage circuit of the A/C clutch relay with a test lamp that is connected to a good ground. Does the test lamp illuminate?	Go to Step 5	Go to Step 9
5	Connect a test lamp between the control circuit of the A/C clutch relay and the ignition 1 voltage circuit of the A/C clutch relay. Start the engine. Command the A/C Relay ON and OFF with a scan tool. Does the test lamp turn ON and OFF with each command?	Go to Step 10	Go to Step 6
6	Does the test lamp remain illuminated with each command?	Go to Step 8	Go to Step 7
7	Test the A/C clutch relay control circuit for the following conditions: An open A high resistance A short to voltage Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 14	Go to Step 11
8	Test the A/C clutch relay control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 14	Go to Step 11
9	Repair the open or the short to ground in the ignition 1 voltage circuit of the A/C clutch relay. Refer to Wiring Repairs in Wiring Systems. Replace the fuse as necessary. Did you complete the repair?	Go to Step 14	-
10	Test for an intermittent and for a poor connection at the A/C clutch relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 14	Go to Step 12
11	Test for an intermittent and for a poor connection at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition?	Go to Step 14	Go to Step 13
12	Replace the A/C clutch relay. Refer to Relay Replacement (Within an Electrical Center) or Relay Replacement (Attached to Wire Harness) in Wiring Systems. Did you complete the replacement?	Go to Step 14	-
13	Replace the ECM. Refer to the appropriate procedure: Engine Control Module (ECM) Replacement in Engine Controls - 1.6L (L91). Did you complete the replacement?	Go to Step 14	-
14	Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate he vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition?	Go to Step 2	Go to Step 15
15	Observe the capture info with a scan tool. Are there any DTCs that have not been diagnosed?	Go to Diagnostic Trouble Code (DTC) List	System OK