Operation CHARM: Car repair manuals for everyone.
Home >> Dodge or Ram Truck >> 2013 >> RAM 1500 Truck 2WD V6-3.6L >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> P Code Charts >> P0642 >> Powertrain Control Module (PCM)

Powertrain Control Module (PCM)






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.

- When Monitored:
With the ignition on.

- Set Condition:
When the Powertrain Control Module (PCM) recognizes the Primary 5-Volt Supply circuit voltage is too low. One Trip Fault. ETC light is flashing. If the vehicle is equipped with the stop/start feature, the system will be disabled when this DTC is active.





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

Diagnostic Test

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

- Go To 2

No

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

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 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

- Go To 3

No

- Repair the (F855) 5-Volt Supply circuit for a short to ground.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

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

- Go To 4

No

- Repair the (K852) 5-Volt Supply circuit for a short to ground.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

4. THROTTLE BODY ASSEMBLY
1. Reconnect all of the harness connectors 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

- Go To 5

No

- Verify that there is good pin to terminal contact in the Throttle Body Assembly and Powertrain Control Module connectors. If OK, replace the Throttle Body Assembly. Throttle Body - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

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

- Go To 6

No

- Verify that there is good pin to terminal contact in the CKP Sensor and Powertrain Control Module connectors. If OK, replace the Crankshaft Position Sensor. Crankshaft Position Sensor - Removal
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

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

- Go To 7

No

- Verify that there is good pin to terminal contact in the Oil Pressure Sensor and Powertrain Control Module connectors. If OK, replace the Oil Pressure Sensor. Oil Pressure Sensor - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

7. A/C PRESSURE TRANSDUCER
1. Turn the ignition off.
2. Disconnect the A/C Pressure Transducer harness connector.
3. Turn the ignition on.
4. Measure the voltage at the (F855) 5-Volt Supply circuit at the A/C Pressure Transducer harness connector.

Is the voltage below 4.75 volts?

Yes

- Go To 8

No

- Verify that there is good pin to terminal contact in the A/C Pressure Transducer and Powertrain Control Module connectors. If OK, replace the A/C Pressure Transducer. A/C Pressure Transducer - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

8. 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

- Go To 9

No

- Verify that there is good pin to terminal contact in the Accelerator Pedal Position Sensor and Powertrain Control Module connectors. If OK, replace the Accelerator Pedal Position Sensor. Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

9. 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

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

No

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

pro multis · About Operation CHARM