P0646
P0646-A/C CONTROL CIRCUIT LOW
For a complete wiring diagram, refer to the Wiring Information Electrical Diagrams.
- When Monitored:
With the engine running and battery voltage greater than 10.4 volts.
- Set Condition:
The Powertrain Control Module (PCM) detects that the A/C Compressor control circuit voltage is below the minimum acceptable value.
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.
1. DTC IS ACTIVE
1. Start the engine and allow it to reach normal operating temperature.
2. Turn the Air Conditioning on.
WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.
3. With the scan tool, select View DTCs.
Is the status Active for this DTC?
Yes
- Go To 2
No
- Perform the CHECKING FOR AN INTERMITTENT DTC diagnostic procedure. Checking for an Intermittent DTC.
2. (Z909) GROUND CIRCUIT OPEN OR HIGH RESISTANCE
1. Turn the ignition off.
2. Disconnect the A/C Compressor connector.
3. Turn the ignition on.
4. Using a 12-volt test light connected to 12 volts, check the (Z909) Ground circuit in the A/C Compressor harness connector.
NOTE: The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.
Is the test light illuminated and bright?
Yes
- Go To 3
No
- Repair the (Z909) Ground circuit for an open circuit or high resistance.
- Perform the PCM VERIFICATION TEST. PCM Verification Test.
3. (C27) A/C COMPRESSOR CONTROL CIRCUIT SHORTED TO GROUND
1. Turn the ignition off.
2. Disconnect the Powertrain Control Module (PCM) harness connector.
3. Measure the resistance between ground and the (C27) A/C Compressor Control circuit in the A/C Compressor harness connector.
Is the resistance below 100 Ohms?
Yes
- Repair the (C27) A/C Compressor Control circuit for a short to ground.
- Perform the PCM VERIFICATION TEST. PCM Verification Test.
No
- Go To 4
4. (C27) A/C COMPRESSOR CONTROL CIRCUIT OPEN OR HIGH RESISTANCE
1. Measure the resistance of the (C27) A/C Compressor Control circuit between the A/C Compressor harness connector and the Powertrain Control Module (PCM) harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go To 5
No
- Repair the (C27) A/C Compressor Control circuit for an open circuit or high resistance.
- Perform the PCM VERIFICATION TEST. PCM Verification Test.
5. A/C COMPRESSOR
1. Connect the Powertrain Control Module (PCM) harness connector.
2. Turn the ignition on.
3. With the scan tool, actuate the A/C Compressor control to the ON position.
4. Using a 12-volt test light connected to ground, check the (C27) A/C Compressor Control circuit in the A/C Compressor harness connector.
NOTE: The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.
5. With the scan tool, actuate the A/C Compressor control to the OFF position.
6. Using a 12-volt test light connected to ground, check the (C27) A/C Compressor Control circuit in the A/C Compressor harness connector.
NOTE: The test light should not be illuminated.
Is the test light illuminated and bright with the actuation ON (100%) and not illuminated with the actuation OFF (0%)?
Yes
- Replace the A/C Compressor.
- Perform the PCM VERIFICATION TEST. PCM Verification Test.
No
- Go To 6
6. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the A/C Compressor and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched, or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals.
4. Search for any Technical Service Bulletins that may apply.
Were any problems found?
Yes
- Repair as necessary.
- Perform the PCM VERIFICATION TEST. PCM Verification Test.
No
- Replace and program the Powertrain Control Module (PCM).
- Perform the PCM VERIFICATION TEST. PCM Verification Test.