P0646

P0646-A/C CONTROL CIRCUIT LOW





For a complete wiring diagram 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. Initial Inspection and Diagnostic Overview


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 (DIESEL). 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 (DIESEL). 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 (DIESEL). 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 (DIESEL). Powertrain Verification Test


No


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