GPEC
P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW
For a complete wiring diagram Consult Diagrams/Electrical.
- When Monitored:
With the ignition on.
- Set Condition:
The PCM detects that the 5 volt supply circuit voltage is below the minimum acceptable value. One Trip Fault. ETC light is flashing.
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Initial Inspection and Diagnostic Overview.
Diagnostic Test
1. DTC IS ACTIVE
NOTE: Improperly installed aftermarket accessories can cause this DTC to set. Check for any improperly installed aftermarket accessories before continuing with this test.
Start the engine and allow it to idle for at least 60 seconds.
WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.
With a scan tool, select View DTCs.
Is the status Active for this DTC?
Yes
- Go to 2
No
- Refer to the *CHECKING FOR AN INTERMITTENT DTC Diagnostic Procedure.Checking For An Intermittent DTC
2. (F855) 5 VOLT SUPPLY CIRCUIT SHORTED TO GROUND
Turn the ignition off.
Disconnect the connector from each sensor that shares the (F855) 5 Volt Supply.
Disconnect all of the Powertrain Control Module (PCM) connectors.
Measure the resistance between ground and the (F855) 5 Volt Supply circuit in the Crankshaft Position Sensor harness connector.
Is the resistance above 100 ohms?
Yes
- Go to 3
No
- Repair the (F855) 5 Volt Supply circuit for a short to ground.
- Perform the PCM Verification Test.Powertrain Verification Test
3. (F855) 5 VOLT SUPPLY CIRCUIT VOLTAGE
Turn the ignition off.
Connect all of the Powertrain Control Module (PCM) connectors.
Turn the ignition on.
Measure the voltage of the (F855) 5 Volt Supply circuit in the Crankshaft Position Sensor harness connector.
Is the voltage above 4.5 volts?
Yes
- Go to 4
No
- Go to 6
4. CRANKSHAFT POSITION SENSOR
Turn the ignition off.
Connect the connector from each sensor or component that shares the (F855) 5 Volt Supply except for the Crankshaft Position Sensor connector.
Turn the ignition on.
Measure the voltage of the (F855) 5 Volt Supply circuit in the Crankshaft Position Sensor harness connector.
Is the voltage above 4.5 volts?
Yes
- Replace the Crankshaft Position Sensor.
- Perform the PCM Verification Test.Powertrain Verification Test
No
- Go to 5
5. SENSOR SHORTED INTERNALLY
CAUTION: You must turn the ignition OFF when connecting or disconnecting a sensor or component connector, then turn the ignition ON when checking the circuit voltage.
Measure the voltage on the (F855) 5 Volt Supply circuit at the Crankshaft Position Sensor harness connector.
Disconnect the connector for each sensor or component that shares the (F855) 5 Volt Supply circuit, one at a time, and note the circuit voltage.
Is the voltage above 4.5 volts when disconnecting any of the sensors?
Yes
- Replace the internally shorted sensor or component.
- Perform the PCM Verification Test.Powertrain Verification Test
No
- Go to 6
6. CHECKING THE PCM POWER AND GROUND CIRCUITS
Perform the diagnostic procedure for *CHECKING THE PCM POWER AND GROUND CIRCUITS. Checking the PCM Power and Ground Circuits
Were any problems found?
Yes
- Repair the PCM power and ground circuit(s) as necessary.
- Perform the PCM Verification Test.Powertrain Verification Test
No
- Go to 7
7. POWERTRAIN CONTROL MODULE (PCM)
Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between all applicable components and the Powertrain Control Module (PCM).
Look for any chafed, pierced, pinched, or partially broken wires.
Look for broken, bent, pushed out or corroded terminals.
Search for any Technical Service Bulletins that may apply.
Were any problems found?
Yes
- Repair as necessary.
- Perform the PCM Verification Test.Powertrain Verification Test
No
- Replace and program the Powertrain Control Module (PCM).
- Perform the PCM Verification Test.Powertrain Verification Test