P0646

P0646-A/C CONTROL CIRCUIT LOW

For a complete wiring diagram, refer to the Wiring Information.

Theory of Operation

The Powertrain Control Module (PCM) receives various information from the operator controls and A/C system to determine when the A/C Compressor Clutch should be turned on. The Totally Integrated Power Module (TIPM) receives a signal from the PCM to turn on the A/C Compressor Clutch. The TIPM supplies 12 Volts to the A/C Compressor Clutch which has a dedicated ground circuit. You will not receive a MIL lamp for this fault, but the customer may complain of poor A/C performance.

- When Monitored:
When the ignition is on.

- Set Condition:
When the signal from the A/C Compressor Clutch circuit output does not match the signal from the A/C Clutch feedback.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

1. CHECK THE (C13) A/C COMPRESSOR CLUTCH CONTROL CIRCUIT FOR AN OPEN/HIGH RESISTANCE
1. Turn the ignition off.
2. Disconnect the PCM C2 harness connector.
3. Disconnect the TIPM C1 harness connector.

NOTE: Check connectors - Clean/repair as necessary.

4. Measure the resistance of the (C13) A/C Compressor Clutch Control circuit between the PCM C2 and TIPM C1 harness connectors.

Is the resistance below 5.0 Ohms?

No

- Repair the (C13) A/C Compressor Clutch Control circuit for an open or high resistance.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

Yes

- Go To 2

2. CHECK THE (C13) A/C COMPRESSOR CLUTCH CIRCUIT FOR A SHORT TO GROUND
1. Ignition off.
2. Measure the resistance between ground and the (C13) A/C Compressor Clutch Control circuit at the TIPM C1 harness connector.

Is the resistance below 10k Ohms?

Yes

- Go To 3

No

- Repair the (C13) A/C Compressor Clutch Control circuit for a short to ground.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

3. CHECK THE PCM/TIPM
1. Reconnect the PCM C2 harness connector.
2. Ignition on, engine not running.
3. Using a 12-Volt test light connected to battery positive, probe the (C13) A/C Clutch Control circuit at the TIPM C1 harness connector while actuating the A/C Compressor Clutch circuit with the scan tool.

NOTE: The test light must illuminate brightly.

4. Compare the brightness to that of a direct connection to the Battery.

Does the test light illuminate brightly?

Yes

- Replace the Totally Integrated Power Module (TIPM).
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Replace the Powertrain Control Module.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.