P0642

P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW





For a complete wiring diagram, refer to the Wiring Information.

- When Monitored:
With the ignition on.

- Set Condition:
The Powertrain Control Module (PCM) detects low voltage on the 5-Volt supply circuit.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

1. DTC IS ACTIVE
1. Attempt to start the engine. If the engine will not start, crank the engine for five 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 may result in possible serious or fatal injury.

2. With the scan tool, select View DTCs.

Is the status Active for this DTC?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test.

2. (F855) PRIMARY 5 VOLT SUPPLY VOLTAGE CHECK




1. Turn the ignition off.
2. Disconnect the Throttle Body harness connector.
3. Turn the ignition on.
4. Measure the voltage of the (F855) 5 Volt Supply circuit in the Throttle Body harness connector.

Is the voltage between 4.7 and 5.2 volts?

Yes

- Go To 3

No

- Go To 4

3. THROTTLE BODY




1. Turn the ignition off.
2. Connect the Throttle Body harness connector.
3. Disconnect the Camshaft 1/2 Position Sensor harness connector.
4. Turn the ignition on.
5. Measure the voltage of the (F855) 5 Volt Supply circuit at the Camshaft 1/2 Position Sensor harness connector.

Is the voltage between 4.7 and 5.2 Volts?

Yes

- Replace the Throttle Body because the Throttle Body is pulling the 5 volt supply low.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 8

4. CAMSHAFT 1/2 POSITION SENSOR




1. Turn the ignition off.
2. Disconnect the Camshaft 1/2 Position Sensor harness connector.
3. Turn the ignition on.
4. Continue measuring the voltage of the (F855) 5 Volt Supply circuit at the Throttle Body harness connector.

Is the voltage between 4.7 and 5.2 Volts?

Yes

- Replace the Camshaft 1/2 Position Sensor.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 5

5. CRANKSHAFT POSITION SENSOR




1. Turn the ignition off.
2. Disconnect the Crankshaft Position Sensor harness connector.
3. Turn the ignition on.
4. Continue measuring the voltage of the (F855) 5 Volt Supply circuit at the Throttle Body harness connector.

Is the voltage between 4.7 and 5.2 Volts?

Yes

- Replace the Crankshaft Position Sensor.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 6

6. ACCELERATOR PEDAL POSITION SENSOR




1. Turn the ignition off.
2. Disconnect the APP Sensor harness connector.
3. Turn the ignition on.
4. Continue measuring the voltage of the (F855) 5 Volt Supply circuit at the Throttle Body harness connector.

Is the voltage between 4.7 and 5.2 Volts?

Yes

- Replace the Throttle Body.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 7

7. 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND




1. Turn the ignition off.
2. Disconnect the PCM harness connectors.
3. Measure the resistance between ground and the (F855) 5-Volt Supply circuit.
4. Measure the resistance between ground and the (K852) 5-Volt Supply circuit.

Is the resistance above 1000 Ohms for both circuits?

Yes

- Go To 8

No

- Repair the 5-Volt Supply circuit for a short to ground.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

8. POWERTRAIN CONTROL MODULE (PCM)
1. Inspect the (F855) 5-Volt Supply circuit between the Camshaft 1/2 Position Sensor harness connector and the PCM harness connector.
2. Inspect the (F855) 5-Volt Supply circuit between the Crankshaft Position Sensor harness connector and the PCM harness connector.
3. Inspect the (F855) 5-Volt Supply circuit between the Throttle Body harness connector and the PCM harness connector.
4. Inspect the (K852) 5-Volt Supply circuit between the Accelerator Pedal Position Sensor harness connector and the PCM harness connector.
5. If the vehicle is equipped with a manual transmission, inspect the (F856) 5-Volt Supply circuit between the Vehicle Speed Sensor harness connector and the PCM harness connector.
6. Look for any chafed, pierced, pinched, or partially broken wires.
7. Look for broken, bent, pushed out or corroded terminals.
8. Perform any Technical Service Bulletins that may apply.

Were any problems found?

Yes

- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Replace and program the Powertrain Control Module (PCM). Powertrain Control Module - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.