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Test Description

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The numbers below refer to the step numbers on the diagnostic table.

  1. 2:  Listen for an audible click when the A/C compressor clutch relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
  2. 3:  This step tests for voltage at the coil side of the A/C compressor clutch relay. The 10-amp fuse supplies power to the coil side of the A/C compressor clutch relay.
  3. 4:  This step verifies that the engine control module is providing ground to the A/C compressor clutch relay. If light always on circuit shorted to ground.
  4. 8:  This step tests for a short to voltage or an open.
  5. 10:  If the A/C fuse is open be sure to test the A/C compressor clutch supply voltage circuit for a short to ground.
DTC P0645

Step Action Yes No
Schematic Reference: HVAC Schematics 
Connector End View Reference: HVAC Connector End Views 
1 Did you perform the Diagnostic System Check - Vehicle? Go to Step 2  Go to Diagnostic System Check - Vehicle
2 
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the A/C Relay ON and OFF in the engine control module (ECM) Special Functions, Engine Output Controls list.
Does the A/C Relay turn ON and OFF with each command?		 Go to Testing for Intermittent Conditions and Poor Connections Go to Step 3 
3 
  1. Turn OFF the ignition.
  2. Disconnect the A/C compressor clutch relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the battery positive voltage circuit of the A/C compressor clutch relay with a test lamp that is connected to a good ground.
Does the test lamp illuminate?		 Go to Step 4  Go to Step 8 
4 
  1. Connect a test lamp between the control circuit of the A/C compressor clutch relay and the battery positive voltage circuit of the A/C compressor clutch relay.
  2. Start the engine.
  3. With a scan tool, command the A/C Relay ON and OFF.
Does the test lamp turn ON and OFF with each command?		 Go to Step 6  Go to Step 5 
5 Test the control circuit of the A/C compressor clutch relay for a short to ground, short to voltage, or an open. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 Go to Step 11  Go to Step 7 
6 Inspect for poor connections at the A/C compressor clutch relay. Refer to Testing for Intermittent Conditions and Poor Connections andConnector Repairs .
Did you find and correct the condition?		 Go to Step 11  Go to Step 9 
7 Inspect for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 Go to Step 11  Go to Step 10 
8  Repair the battery positive voltage circuit of the A/C compressor clutch relay. Refer to Wiring Repairs .
Did you complete the repair?		 Go to Step 11  -
9 Replace the A/C compressor clutch relay.
Did you complete the replacement?		 Go to Step 11  -
10  Replace the ECM. Refer to Control Module References for replacement, setup and programming.
Did you complete the replacement?		 Go to Step 11  -
11
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC reset?		 Go to Step 2  System OK
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