← Back to list

2014 Ford E350 Superduty RV Model P0642 Code: Sensor Reference Voltage 'A' Circuit Low Diagnosis

Model: 2014 E350 Superduty (RV) Fault Code: P0642 Posted: 2021-05-10 18:21

I own a 2014 Ford E350 Superduty chassis with an RV trailer mounted on the rear. The vehicle is displaying a P0642 diagnostic trouble code — "Sensor Reference Voltage 'A' Circuit Low." I previously encountered a U0109 code indicating lost communication with the Fuel Pump Control Module, which I resolved by replacing the fuel pump module. After replacement and clearing the codes, the U0109 no longer appears. However, the P0642 code reappears every time I reset the system. This suggests a persistent issue in the reference voltage circuit. I am currently attempting to locate the 'A' reference circuit for the sensor voltage, so I can trace the wiring harness for potential shorts or faulty sensors. While I've reviewed online resources and subscribed to AllDiyData, I'm unable to find specific references to Circuit A in the vehicle's schematics. My goal is to identify whether a shorted wire or malfunctioning sensor is causing the P0642 code. The engine starts, runs smoothly, and drives without any performance issues — indicating that the Powertrain Control Module (PCM) itself may not be faulty. I believe the issue lies in the wiring or one of the sensors connected to the 5V reference circuits. Any guidance on identifying these circuits or troubleshooting steps would be greatly appreciated.

Related fault codes
P0642
Comments (6)
Anonymous 2021-05-10 19:26

The Powertrain Control Module (PCM) should have labeled 5V reference circuits. A shorted sensor or wiring harness connected to this circuit is likely the root cause of the P0642 code.

Anonymous 2021-05-12 14:31

Thanks for the input — I'm focused on locating the specific 5V reference circuits. Given that the vehicle runs normally and starts reliably, it's unlikely the PCM is faulty. The issue probably stems from a shorted wire or sensor in one of the 5V reference circuits. If I can identify these circuits at the PCM end, that would help narrow down the problem.

Anonymous 2021-05-12 16:24

Try using a scan tool to perform a code reset instead of simply disconnecting the battery. A full KAM (Key Access Module) clear via scan tool may be more effective than a simple battery disconnection.

Anonymous 2021-05-13 15:22

I've already tried both methods — battery disconnect and scan tool reset — and in each case, the P0642 code returns immediately after the system is cleared.

Anonymous 2021-05-14 09:07

On the Alldata wiring schematic, reference sensors such as TPS (Throttle Position Sensor), MAF (Mass Airflow Sensor), CAM (Camshaft Position Sensor), and CRK (Crankshaft Position Sensor) are typically connected to 5V reference circuits. Use your scan tool to monitor live data from these sensors — look for abnormal readings or signal drops that could trigger the P0642 code. I don't have exact voltage specifications, but this should help identify potential issues in the circuit.

Anonymous 2021-05-14 11:36

Thank you for the helpful direction. I will review the live data from the TPS, MAF, CAM, and CRK sensors to see if any of them show abnormal readings that could be linked to the P0642 code.