P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW
For a complete wiring diagram Refer to Section 8W
Possible Causes
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INTERMITTENT DTC
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5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
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BOOST PRESSURE SENSOR
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FUEL PRESSURE SENSOR
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CAMSHAFT POSITION SENSOR
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ENGINE CONTROL MODULE (ECM)
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Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
(Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)
Theory of Operation
The ECM contains 3 internal 5–Volt Sensor Supply sources. Each 5–Volt Supply source is split into parallel circuits to provide 5 volts to multiple sensors. Sensor Supply 1 provides
5 volts to the Camshaft Position Sensor, Boost Pressure Sensor and the Fuel Pressure Sensor.
Diagnostic Test
1.
CHECK FOR ACTIVE DTC
Turn the ignition on.
With the scan tool, erase ECM DTCs.
With the scan tool, View DTCs.
Is the status Active for this DTC?
Yes
No
2.
CAMSHAFT POSITION SENSOR
Turn the ignition off.
Disconnect the CMP Sensor harness connector.
Turn the ignition on.
Measure the voltage of the (K844) Camshaft Position Sensor 5 Volt Supply circuit at the CMP Sensor harness connector.
Is the voltage above 4.6 volts?
Yes
No
3.
BOOST PRESSURE SENSOR
Turn the ignition off.
Disconnect the Boost Pressure Sensor harness connector.
Turn the ignition on.
Measure the voltage of the (K356) Boost Pressure Sensor 5 Volt Supply circuit at the Boost Pressure Sensor harness connector.
Is the voltage above 4.6 volts?
Yes
No
4.
FUEL PRESSURE SENSOR
Turn the ignition off.
Disconnect the Fuel Pressure Sensor harness connector.
Turn the ignition on.
Measure the voltage of the (K350) Fuel Pressure Sensor 5 Volt Supply circuit at the Fuel Pressure Sensor harness connector.
Is the voltage above 4.6 volts?
Yes
No
5.
5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
Turn the ignition off.
Disconnect the ECM harness connectors.
Measure the resistance between ground and the (K356) Boost Pressure Sensor 5 Volt Supply circuit at the Boost Pressure Sensor harness connector.
Measure the resistance between ground and the (K844) Camshaft Position Sensor 5 Volt Supply circuit at the CMP Sensor harness connector.
Measure the resistance between ground and the (K350) Fuel Pressure Sensor 5 Volt Supply circuit at the Fuel Pressure Sensor harness connector.
Is the resistance above 1000 ohms for each circuit?
Yes
No
6.
ENGINE CONTROL MODULE (ECM)
Inspect the (K844) Camshaft Position Sensor 5 Volt Supply circuit between the CMP harness connector and the ECM harness connector.
Inspect the (F855) Boost Pressure Sensor 5 Volt Supply circuit between the Boost Pressure Sensor harness connector and the ECM harness connector
Inspect the (F855) Fuel Pressure Sensor 5 Volt Supply circuit between the Fuel Pressure Sensor harness connector and the ECM harness connector
Look for any chafed, pierced, pinched, or partially broken wires.
Look for broken, bent, pushed out or corroded terminals.
Monitor the scan tool data relative to this circuit and wiggle test the wiring and connectors.
Look for the data to change or for the DTC to reset during the wiggle test.
Refer to any Technical Service Bulletins that may apply.
Were any problems found?
Yes
No