FixItFor.Us
P codepowertrainHigh severity

P027AFuel Pump "B" Module Control Circuit/Open

The computer has lost or detected a fault in the control circuit to the secondary ("B") fuel pump module.

Definition

Vehicles with dual fuel pumps or a dedicated fuel pump driver/control module for the secondary pump use a control circuit between the PCM and that module. P027A sets when the PCM detects an open or general malfunction on the fuel pump "B" module control circuit — the command signal is not reaching or being acknowledged by the module. Depending on the system, symptoms range from no noticeable change at light load to fuel starvation, low power at high demand, extended cranking, or a no-start, with the MIL illuminated.

Common causes

  • Open or chafed wiring in the control circuit between the PCM and the fuel pump B module
  • Corroded or backed-out terminals at the pump module connector (often exposed near the tank or frame)
  • Failed fuel pump driver/control module
  • Blown fuse or lost power/ground feed to the module
  • Water intrusion into a module mounted on the frame or under the vehicle
  • Faulty PCM output for the pump control signal (least common)

Common misdiagnoses

  • Replacing the in-tank fuel pump when the driver module or its wiring is the fault
  • Replacing the fuel filter for a fuel delivery complaint that is electrical
  • Replacing the PCM before checking module power, ground, and control wiring
  • Condemning fuel pump A components when the fault is isolated to the B circuit

Troubleshooting steps

  1. 1.Locate and inspect the pump B module

    Find the secondary pump driver module (commonly frame- or tank-mounted) and inspect for corrosion, water intrusion, and connector damage — corroded frame-mounted modules are a classic failure.

  2. 2.Verify module power and ground

    Key on, confirm battery voltage at the module feed and less than 0.1 V drop on its ground under load.

  3. 3.Test the control signal

    Scope the PCM-to-module control wire (often a PWM/duty-cycle signal) while cranking and confirm the command is present at the module connector.

  4. 4.Check circuit continuity

    With both ends disconnected, verify the control wire has near-zero ohms end to end and no shorts to ground or power.

  5. 5.Confirm pump operation when commanded

    If command, power, and ground are all good at the module but the pump does not run, replace the module; verify pump B pressure/flow contribution afterward.

  6. 6.Clear codes and load-test

    Clear the DTC and road test under high fuel demand (heavy acceleration or towing conditions) to confirm the circuit fault does not return.

Related codes