Diagnostic Test - Fuel Pump PWM Control Circuit Faults (P0628, P0629, P1205, P120B, P2633, P2634)

TECH TIP:  The FPCM DTCs will set incorrectly for some vehicles/model years due to incorrect calibrations. For those vehicles it is best to perform the "COMPLETE FUEL PUMP CONTROL MODULE SYSTEM TESTING (NOT DTC SPECIFIC)" diagnostic procedure. Refer to the "KNOW ISSUES" information above for a list of the vehicles with incorrect calibrations.

FUEL PUMP PWM CONTROL CIRCUIT OPEN/LOW/HIGH (P0628, P0629, P1205, P120B, P2633, P2634):  There should be a relatively constant voltage on the fuel pump control circuit. When the system is operating normally without any faults the output voltage is typically around 7.0 - 9.0 volts. When there is a fault in the system the output is typically higher due to the FPCM defaulting to a higher output (between 10.5 volts and battery voltage). For this reason the fuel pump output voltage may be high near battery voltage due to an issue in the Fuel Pump circuits or one of the other FPCM circuits (Command or Feedback). If one of those circuits indicates an issue or has a DTC set against it, diagnose that circuit before continuing with the diagnosis of the fuel pump circuits.

The test method listed below can be performed using the Mopar Scope or with a meter.

Courtesy of CHRYSLER GROUP, LLC

1. Back probe the fuel pump PWM control circuit and fuel pump ground circuit at the fuel pump harness connector. Crank or start the engine while monitoring the voltage on both circuits. The red channel on the pattern above shows the normal output to the fuel pump on the fuel pump PWM control from the FPCM. The fuel pump PWM control circuit voltage is typically around 7.0 - 9.0 volts. The ground circuit should have 0 volts and the pump should operate if the pump and circuits are working properly. Select the result that best matches the voltage readings.
   1. The voltage on both circuits reads as described above and the fuel pump is running, the fuel pump and circuits are operating normally.
      • The issue could be either an intermittent condition, poor pin fit at a connector, or a calibration issue setting the incorrect DTC. If the terminals appear good and an intermittent issue isn't found perform the "DIAGNOSTIC TEST - COMPLETE FUEL PUMP CONTROL MODULE SYSTEM TESTING (NOT DTC SPECIFIC)" diagnostic to check the entire system operation.
   2. The voltage on both circuits reads as described above but the fuel pump does not operate, the fuel pump is faulty.
      • Replace the fuel pump in accordance with the service information.
   3. There is equal voltage present on both the fuel pump PWM control circuit and ground circuit. Example: 10 volts on both circuits.
      • Repair the ground circuit for an open. NOTE: The fuel pump ground circuit grounds through the FPCM chassis ground circuit. this condition may also be accompanied by a loss of communication DTC. This will likely lead to a no start with no fuel pump operation. 
   4. If the fuel pump PWM control circuit and ground circuit voltage is 0 at the Fuel Pump harness connector, the fuel pump PWM control circuit is open or shorted to ground. Repair the circuit for an open or short to ground. NOTE: A short to ground in the fuel pump PWM control circuit may cause the fuse to open for the FPCM Battery voltage supply from the relay, which can cause a Loss of Communication fault also. This will lead to a no start with no fuel pump operation. 
   5. The fuel pump PWM control circuit is reading battery voltage and the fuel pump ground circuit voltage is 0 volts. Either there is a fault with another circuit or the fuel pump PWM control circuit is shorted to battery voltage.
      • The condition will most likely occur due to a fault in the command or feedback circuit. Perform the "DIAGNOSTIC TEST - COMPLETE FUEL PUMP CONTROL MODULE SYSTEM TESTING (NOT DTC SPECIFIC)" diagnostic to check the entire system operation. If the command and feedback circuits are functioning properly and the voltage supply to the FPCM is good, the fuel pump PWM control circuit is likely shorted to battery voltage. Repair the circuit for a short to voltage.