P0642

P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW





For a complete wiring diagram refer to Diagrams/Electrical.

- When Monitored:

With the ignition on.

- Set Condition:

The PCM detects low voltage on the 5 volt supply circuit.






Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test

1. DTC IS ACTIVE

Attempt to start the engine. If the engine will not start, crank the engine for 5 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 the 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. ACCELERATOR PEDAL POSITION SENSOR





Turn the ignition off.

Disconnect the APP Sensor harness connector.

Turn the ignition on.

Measure the voltage of the (F856) 5 Volt Supply circuit in the APP Sensor harness connector.

Is the voltage above 4.6 volts?

Yes

- Replace the Accelerator Pedal Position Sensor.
- Perform the PCM Verification Test Ver. 1. PCM Verification Test

No

- Go to 3

3. CAMSHAFT 1/2 POSITION SENSOR





Turn the ignition off.

Disconnect the Camshaft 1/2 Position Sensor harness connector.

Turn the ignition on.

Measure the voltage of the (F855) 5 Volt Supply circuit.

Is the voltage above 4.6 volts?

Yes

- Replace the Camshaft 1/2 Position Sensor.
- Perform the PCM Verification Test Ver. 1. PCM Verification Test

No

- Go to 4

4. CRANKSHAFT POSITION SENSOR





Turn the ignition off.

Disconnect the Crankshaft Position Sensor harness connector.

Turn the ignition on.

Measure the voltage of the (F855) 5 Volt Supply circuit.

Is the voltage above 4.6 volts?

Yes

- Replace the Crankshaft Position Sensor.
- Perform the PCM Verification Test Ver. 1. PCM Verification Test

No

- Go to 5

5. THROTTLE POSITION SENSOR





Turn the ignition off.

Disconnect the Throttle Body harness connector.

Turn the ignition on.

Measure the voltage of the (F855) 5 Volt Supply circuit.

Is the voltage above 4.6 volts?

Yes

- Replace the Throttle Body.
- Perform the PCM Verification Test Ver. 1. PCM Verification Test

No

- Go to 6

6. VEHICLE EQUIPPED WITH MANUAL TRANSMISSION

Is the vehicle equipped with a manual transmission?

Yes

- Go to 7

No

- Go to 8

7. VEHICLE SPEED SENSOR

NOTE: Only vehicles equipped with a manual transmission will use a Vehicle Speed Sensor.

Turn the ignition off.

Disconnect the Vehicle Speed Sensor harness connector.

Turn the ignition on.

Measure the voltage of the (F856) 5 Volt Supply circuit.

Is the voltage above 4.6 volts?

Yes

- Replace the Vehicle Speed Sensor.
- Perform the PCM Verification Test Ver. 1. PCM Verification Test

No

- Go to 8

8. 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND





Turn the ignition off.

Disconnect the PCM harness connectors.

Measure the resistance between ground and the (F855) 5 Volt Supply circuit.

Measure the resistance between ground and the (F856) 5 Volt Supply circuit.

Is the resistance above 1000 ohms for both circuits?

Yes

- Go to 9

No

- Repair the 5 Volt Supply circuit for a short to ground.
- Perform the PCM Verification Test Ver. 1. PCM Verification Test

9. POWERTRAIN CONTROL MODULE (PCM)

Inspect the (F855) 5 Volt Supply circuit between the Camshaft 1/2 Position Sensor harness connector and the PCM harness connector.

Inspect the (F855) 5 Volt Supply circuit between the Crankshaft Position Sensor harness connector and the PCM harness connector.

Inspect the (F855) 5 Volt Supply circuit between the Throttle Body harness connector and the PCM harness connector.

Inspect the (F856) 5 Volt Supply circuit between the Accelerator Pedal Position Sensor harness connector and the PCM harness connector.

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.

Look for any chafed, pierced, pinched, or partially broken wires.

Look for broken, bent, pushed out or corroded terminals.

Refer to any Technical Service Bulletins that may apply.

Were any problems found?

Yes

- Repair as necessary.
- Perform the PCM Verification Test Ver. 1. PCM Verification Test

No

- Replace the PCM.
- Perform the PCM Verification Test Ver. 1. PCM Verification Test