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P codepowertrainMedium severity

P027BFuel Pump "B" Module Control Circuit Range/Performance

The PCM has detected that the control signal to the secondary ("B") fuel pump driver module is present but out of its expected range, or the module's feedback does not match the commanded pump duty cycle.

Definition

On vehicles with electronically controlled fuel delivery, the PCM sends a duty-cycle (PWM) command to a fuel pump driver module, which powers the pump; "B" identifies the second pump or module on dual-pump systems such as saddle tanks, diesel lift pumps, or auxiliary high-flow pumps. P027B sets when the control or feedback signal is valid but outside the expected window — for example, the module reports a duty cycle or current draw that disagrees with the PCM's command. Symptoms range from none to long cranking, hesitation under load, or reduced power, and the MIL will illuminate; some applications enter a reduced-power mode to protect the engine from lean operation.

Common causes

  • Corroded or chafed wiring/connector between the PCM and the fuel pump driver module
  • Failing fuel pump driver module (heat- or corrosion-damaged, especially trunk- or frame-mounted units)
  • Poor ground at the fuel pump driver module
  • Weak or worn fuel pump drawing abnormal current through the module
  • Low charging-system voltage skewing the module's control range
  • PCM driver fault (rare)

Common misdiagnoses

  • Fuel pump replaced when the driver module or its wiring is at fault
  • Fuel filter replaced without testing pressure or the control circuit
  • Fuel pressure sensor replaced for what is a control-circuit fault
  • PCM replaced before checking module grounds and connectors

Troubleshooting steps

  1. 1.Record freeze frame and companion codes

    Note whether pump "A" codes, fuel pressure codes (P0087/P0088), or communication codes set at the same time — they point to a system-level cause.

  2. 2.Verify actual fuel pressure

    Compare gauge or scan-tool fuel pressure against the commanded value at idle and under load; a mismatch with a valid command implicates the pump or module, not the PCM.

  3. 3.Inspect the fuel pump driver module and connector

    These modules are often mounted near the tank or in the spare-tire area — look for green corrosion, water intrusion, and rub-through on the harness.

  4. 4.Test module power and ground

    With the circuit loaded, voltage drop on the module's ground should be under 0.1 V and supply should be within 0.5 V of battery voltage.

  5. 5.Scope the control and feedback signals

    Verify a clean PWM square wave from the PCM to the module and a plausible feedback/diagnostic signal back; a ragged or clipped waveform means wiring or module failure.

  6. 6.Substitute the driver module if signals are good

    If command, power, and ground all check out but the pump is not driven correctly, replace the fuel pump driver module and retest under load.

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