P0642
P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOWP0642-Sensor Reference Voltage 1 Circuit Low:
WHEN MONITORED:
Ignition on.
SET CONDITION:
When the PCM recognizes the Primary 5-volt Supply circuit voltage is too low. One Trip Fault. ETC light is flashing.
POSSIBLE CAUSES
- (F855) Primary 5-volt supply shorted to ground
- Sensor shorted to ground
- 5-volt sensor
- PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Diagnostic Test
1. ACTIVE DTC
Ignition on, engine not running.
With a scan tool, read DTCs.
NOTE: Improperly installed aftermarket accessories can cause this DTC to set. Check for wiring added by customer.
Q: Is the DTC active at this time?
YES: Go To 2
NO: Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Component Tests and General Diagnostics
Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
2. (F855) PRIMARY 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
Turn the ignition off.
Disconnect the C2 PCM harness connector.
Disconnect all the Sensors that share the (F855) Primary 5-volt Supply circuit.
Measure the resistance between ground and the (F855) Primary 5-volt Supply circuit in the CKP Sensor harness connector.
Q: Is the resistance below 100 ohms?
YES: Repair the short to ground in the (F855) Primary 5-volt Supply circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 3
3. 5-VOLT SENSOR
Turn the ignition off.
Reconnect all the previously disconnected Sensors except for the CKP Sensor harness connector.
Ignition on, engine not running.
Measure the voltage on the (F855) Primary 5-volt Supply circuit in the CKP Sensor harness connector.
Q: Is the voltage below 4.5 volts?
YES: Go To 4
NO: Replace the CKP Sensor. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
4. 5-VOLT SENSOR SHORTED TO GROUND
Measure the voltage on the (F855) Primary 5-volt Supply circuit at the CKP Sensor harness connector.
CAUTION: You must Turn the Ignition OFF when disconnecting any of the Sensor harness connectors and Turn the Ignition On to check the voltage readings.
While monitoring the voltage, disconnect each Sensor harness connector that shares the (F855) Primary 5-volt Supply circuit, one at a time.
NOTE: Reconnect all the Sensors and clear all trouble codes before continuing.
Q: Does the voltage increase above 4.5 volts when disconnecting any of the remaining Sensors?
YES: Replace the Sensor that causes the (F855) Primary 5-volt Supply circuit voltage to increase when disconnected. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 5
5. PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Q: Were there any problems found?
YES: Repair as necessary. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Replace and program the Powertrain Control Module. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test