P0642 LOW 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 is below a calibrated value.

• POSSIBLE CAUSES
• FAN CLUTCH ASSEMBLY
• (F856) 5-VOLT SHORTED TO GROUND
• (F856) 5-VOLT SUPPLY SHORTED TO ANOTHER CIRCUIT
• FAN DTC
• INTERMITTENT CONDITION
• ECM

DIAGNOSTIC PROCEDURE

1. Disconnect the Fan clutch harness connector.
   NOTE: Check connectors - Clean/repair as necessary.
   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. Turn the ignition off. Disconnect the ECM harness connector.
   NOTE: Check connectors - Clean/repair as necessary.
   Measure the resistance between the (F856) #2 5-volt supply (fan speed sensor power) circuit in the sensor harness connector and battery negative. Is the resistance greater than 100k Ohms?
   Yes --> Go To 3
   No --> Repair the #2 (F856) 5-volt supply shorted to ground. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
3. Measure the resistance between the sensor (F856) #2 5-volt supply (fan speed sensor power) circuit in the ECM harness connector to all other circuits in the ECM harness connectors Is the resistance greater than 100k Ohms?
   Yes --> Go To 4
   No --> Repair the 5-volt supply shorted to another circuit. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
4. Reconnect the ECM harness connectors. Reconnect the disconnected Fan harness connector. Turn the ignition on. With the DRBIII®, read DTCs. Is DTC P0483 set?
   Yes --> Repair the Fan DTC. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
   No --> Go To 5
5. Turn the ignition off. Disconnect the Fan harness connector. Turn the ignition on. Measure the voltage between the sensor (F856) #2 5-volt supply (fan speed sensor power) circuit at the fan clutch harness connector and the fan speed sensor ground. Is the voltage between 4.5 and 5.5 volts?
   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).