P0643 HIGH VOLTAGE AT THE #2 SENSOR SUPPLY CIRCUIT

When Monitored and Set Condition:

When Monitored: With the key on.
Set Condition: Voltage detected on the #2 sensor supply circuit was above a calibrated value.

POSSIBLE CAUSES

• FAN CLUTCH ASSEMBLY
• (F856) 5-VOLT SHORTED TO VOLTAGE
• INTERMITTENT CONDITION
• ECM

DIAGNOSTIC PROCEDURE

1. Disconnect the Fan clutch harness connector. With the DRBIII®, read DTCs. Did P0483 set?
   Yes --> Replace the Fan clutch assembly. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
   No --> Go To 2
2. Disconnect the ECM harness connectors. Disconnect the Fan harness connector.
   NOTE: Check connectors - Clean/repair as necessary.
   Measure the voltage between the fan speed sensor (F856) 5-volt supply circuit and battery negative. Is the voltage greater than 1 volt?
   Yes --> Repair the (F856) 5-volt supply shorted to voltage. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
   No --> Go To 3
3. Turn the ignition off. Reconnect the ECM harness connectors. Turn the ignition on. Measure the voltage between the (F856) 5-volt supply circuit in the sensor harness connector and battery negative. Is the voltage greater than 6 volts?
   Yes --> Replace the ECM. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
   No --> Refer to the SYMPTOM: INTERMITTENT CONDITION Symptom (Diagnostic Procedure). Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).