2014 Jeep Wrangler JK Factory Service Manual 28 - DTC-Based Diagnostics

P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW

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

Theory of Operation

The Powertrain Control Module (PCM) contains two internal 5-Volt Sensor Supply sources. Each 5-Volt Supply source is split into parallel circuits to provide a 5.0 volt reference to multiple three wire sensors. For self protection, if the 5-Volt Supply circuit is shorted to ground or if one of the sensors is internally shorted, the PCM will turn off the 5-Volt Supply circuit until the next ignition cycle.



Possible Causes

(F855) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
(K852) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
CRANKSHAFT POSITION SENSOR
OIL PRESSURE SENSOR
THROTTLE BODY ASSEMBLY
ACCELERATOR PEDAL POSITION (APP) SENSOR
POWERTRAIN CONTROL MODULE (PCM)

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).


1. ACTIVE DTC



NOTE: Improperly installed aftermarket accessories can cause this DTC to set. Check for any improperly installed aftermarket accessories before continuing with this test.
1. Turn the ignition on for 60 seconds.
2. With a scan tool, read the active DTCs.


Is the DTC Active at this time?

Yes


No


2. CHECK THE (F855) 5-VOLT SUPPLY CIRCUIT FOR A SHORT TO GROUND

1. Turn the ignition off.
2. Disconnect all of the sensor harness connectors that share the (F855) 5-Volt Supply circuit.
3. Disconnect the APP Sensor harness connector.
4. Disconnect the PCM C1 and C2 harness connectors.
5. Measure the resistance between ground and the (F855) 5-Volt Supply circuit at the Throttle Body Assembly harness connector.


Is the resistance above 10k Ohms?

Yes


No


3. CHECK THE (K852) 5-VOLT SUPPLY CIRCUIT FOR A SHORT TO GROUND

1. Measure the resistance between ground and the (K852) 5-Volt Supply circuit at the APP Sensor harness connector.


Is the resistance above 10k Ohms?

Yes


No


4. THROTTLE BODY ASSEMBLY

1. Reconnect the PCM connectors and all of the previously disconnected Sensors except for the Throttle Body Assembly harness connector.
2. Turn the ignition on.
3. Measure the voltage of the (F855) 5-Volt Supply circuit at the Throttle Body Assembly harness connector.


Is the voltage below 4.75 Volts?

Yes


No


5. CRANKSHAFT POSITION SENSOR

1. Turn the ignition off.
2. Disconnect the CKP Sensor harness connector.
3. Turn the ignition on.
4. Measure the voltage at the (F855) 5-Volt Supply circuit at the CKP Sensor harness connector.


Is the voltage below 4.75 volts?

Yes


No


6. OIL PRESSURE SENSOR

1. Turn the ignition off.
2. Disconnect the Oil Pressure Sensor harness connector.
3. Turn the ignition on.
4. Measure the voltage at the (F855) 5-Volt Supply circuit at the Oil Pressure Sensor harness connector.


Is the voltage below 4.75 volts?

Yes


No


7. ACCELERATOR PEDAL POSITION SENSOR

1. Turn the ignition off.
2. Disconnect the APP Sensor harness connector.
3. Turn the ignition on.
4. Measure the voltage at the (K852) 5-Volt Supply circuit at the APP Sensor harness connector.


Is the voltage below 4.75 volts?

Yes


No


8. POWERTRAIN CONTROL MODULE (PCM)

1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the related Sensors and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched, or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the related Sensor and Powertrain Control Module connectors.
4. Perform any Technical Service Bulletins that may apply.


Were there any problems found?

Yes


No