P0646 LOW VOLTAGE DETECTED AT THE A/C CLUTCH RELAY
When Monitored and Set Condition:
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
DIAGNOSTIC PROCEDURE
-
Ignition on, engine not running. With the DRBIII®, actuate the A/C clutch relay. Can you hear the Relay clicking?
Yes --> Go To 2
No --> Go To 3 -
Actuation still running. While the relay is clicking, wiggle the wiring harness and connectors throughout the circuit. Does this interrupt the clicking?
Yes --> Repair the loose connection. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
No --> Go To 3 -
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. Is the resistance less than 100 Ohms?
Yes --> Go To 4
No --> Replace the A/C clutch relay. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). -
Ignition on, engine not running. Measure the voltage on the Fused Battery Supply circuit in the PDC. Is the voltage within 1 volt of battery voltage?
Yes --> Go To 5
No --> Repair the open Fused battery supply. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). -
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. Is the resistance less than 10 Ohms?
Yes --> Go To 6
No --> Repair the open (C13) A/C signal circuit. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). -
Measure the resistance of the (C13) A/C Clutch signal circuit between the PDC and battery negative. Is the resistance greater than 100k Ohms?
Yes --> Go To 7
No --> Repair the (C13) A/C signal circuit shorted to ground. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). -
Reconnect the ECM harness connectors. Using the DRBIII®, actuate the A/C Clutch Relay While monitoring with the DRBIII®, use a jumper wire to connect 12 volts to the relay signal cavity (85) in the PDC with the relay disconnected. Did DTC P0647 set?
Yes --> Refer to the SYMPTOM: INTERMITTENT CONDITION Symptom (Diagnostic Procedure). Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
No --> Replace the ECM. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).