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

1. 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
2. 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
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).
4. 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).
5. 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).
6. 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).
7. 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).