P0646

P0646-LOW VOLTAGE DETECTED AT THE A/C CLUTCH RELAY

P0646 - Low Voltage Detected At The A/C Clutch Relay:

WHEN MONITORED
When the ignition is on.

SET CONDITION
When the signal from the A/C Clutch output does not match the signal from the A/C Clutch feedback.

POSSIBLE CAUSES
- A/C clutch relay
- Loose connection
- Fused battery supply
- (C13) A/C signal circuit open
- (C13) A/C signal circuit shorted to ground
- Intermittent condition
- ECM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test

1. CLUTCH CLICKING
Ignition on, engine not running.
With the scan tool, actuate the A/C clutch relay.

Q: Can you hear the Relay clicking?

YES: Go To 2
NO: Go To 3

2. LOOSE CONNECTION
Actuation still running.
While the relay is clicking, wiggle the wiring harness and connectors throughout the circuit.

Q: Does this interrupt the clicking?

YES: Repair the loose connection. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
NO: Go To 3

3. A/C CLUTCH RELAY





Remove the A/C Clutch Relay from the PDC.

NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance between terminals 85 and 86 of the A/C Clutch Relay.

Q: Is the resistance less than 100 Ohms?

YES: Go To 4
NO: Replace the A/C clutch relay. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1

4. FUSED BATTERY SUPPLY






Ignition on, engine not running.
Measure the voltage on the Fused Battery Supply circuit in the PDC.

Q: Is the voltage within 1 volt of battery voltage?

YES: Go To 5
NO: Repair the open Fused battery supply. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1

5. (C13) A/C SIGNAL CIRCUIT OPEN
Turn the ignition off.
Disconnect the ECM harness connectors.

NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance of the (C13) A/C Clutch signal circuit between the PDC and the ECM harness connector.

Q: Is the resistance less than 10 Ohms?

YES: Go To 6
NO: Repair the open (C13) A/C signal circuit. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1

6. (C13) A/C SIGNAL CIRCUIT SHORTED TO GROUND
Measure the resistance of the (C13) A/C Clutch signal circuit between the PDC and battery negative.

Q: Is the resistance greater than 100k Ohms?

YES: Go To 7
NO: Repair the (C13) A/C signal circuit shorted to ground. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1

7. ECM
Reconnect the ECM harness connectors.
Using the scan tool, actuate the A/C Clutch Relay
While monitoring with the scan tool, use a jumper wire to connect 12 volts to the relay signal cavity (85) in the PDC with the relay disconnected.

Q: Did DTC P0647 set?

YES: Refer to the INTERMITTENT CONDITION Symptom (Diagnostic Procedure).
NO: Replace the ECM. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1