P0646

P0646-A/C CONTROL CIRCUIT LOW





For complete wiring diagrams refer to Diagrams/Electrical.


Theory of Operation

The clutch on the A/C compressor controls the drive of the Freon compressor. The clutch is driven by a signal from the TIPM. The TIPM receives a signal from the ECM. The ECM receives various information from the operator controls and A/C system to determine when the clutch should be turned on. The system will activate the A/C clutch during A/C or defrost use. 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 Clutch circuit output does not match the signal from the A/C Clutch feedback







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test


1. TIPM GROUND OPEN

Ignition on, engine not running.

Using a voltmeter, connect one voltmeter lead to Battery Positive and the other on TIPM ground.

Does the voltmeter show battery voltage?

Yes

- Go To 2

No

- Fix or replace the open circuit in the Battery Return Circuit
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

2. (C13) A/C CLUTCH CONTROL CIRCUIT OPEN

Disconnect the ECM and TIPM connectors.


NOTE: Check connectors - Clean/repair as necessary.

Using an Ohmmeter, measure the resistance of the (C13) A/C Clutch Control circuit between the TIPM and the C2 ECM harness connector.

Is the resistance less than 10 Ohms?

No

- Fix or replace the harness.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

Yes

- Go To 3

3. (C13) A/C CLUTCH CIRCUIT SHORTED TO GROUND





Turn the ignition off.

Measure the resistance between ground and the (C13) A/C Clutch Control circuit at the TIPM harness connector.

Is the resistance greater than 100k Ohms?

Yes

- Go To 4

No

- Fix or replace the harness.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

4. ECM/TIPM





Connect the C2 ECM harness connector.

Ignition on, engine not running.

Using a 12-volt test light connected to battery negative, probe the (C13) A/C Clutch Control circuit at the TIPM harness connector while actuating the A/C clutch circuit with the scan tool.


NOTE: The test light must illuminate brightly.

Compare the brightness to that of a direct connection to the battery.

Does the test light illuminate brightly?

Yes

- Replace the TIPM.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Replace the ECM.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test