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P codepowertrainHigh severity

P027CFuel Pump "B" Module Control Circuit Low

The control circuit for the secondary ("B") fuel pump driver module is stuck at a lower voltage than the PCM expects, usually from a short to ground or a failed module.

Definition

The PCM monitors the voltage on the control line to the "B" fuel pump module and sets P027C when that circuit reads below its acceptable threshold. Because the module may stop driving the pump entirely, symptoms can include a no-start, stalling, loss of power under load, or (on dual-pump systems) normal light-throttle operation with fuel starvation at high demand. The MIL illuminates, and many applications disable the affected pump and log a reduced-power or fail-safe mode until the fault is repaired.

Common causes

  • Control wire shorted to ground (chafed harness near the tank, frame rail, or body pass-through)
  • Failed fuel pump driver module pulling the circuit low internally
  • Corroded or water-contaminated module connector
  • Open circuit on a line the PCM biases high, reading as low
  • PCM driver transistor failure (rare)

Common misdiagnoses

  • Fuel pump replaced when the wiring is shorted to ground
  • Fuel pump relay replaced although this is a module control circuit, not the relay feed
  • Battery or charging system blamed for the stall/no-start
  • PCM replaced before the harness is inspected

Troubleshooting steps

  1. 1.Confirm whether the pump runs

    Listen for the pump prime at key-on or command it with a bidirectional scan tool; no prime with this code points to the control circuit or module.

  2. 2.Check circuit voltage at the module connector

    Backprobe the control line key-on: a reading near 0 V when the PCM should be commanding the pump indicates a short to ground or dead PCM driver.

  3. 3.Isolate the short

    Disconnect the PCM and module, then measure resistance from the control wire to chassis ground — anything under about 10 kΩ means a harness short; infinite resistance shifts suspicion to the module or PCM.

  4. 4.Inspect harness routing and connectors

    Concentrate on areas over the tank, along the frame rail, and at body grommets where insulation rubs through; also check for water in the module connector.

  5. 5.Verify module power and ground before condemning it

    Confirm battery voltage on the supply and less than 0.1 V drop on ground under load; if wiring is proven good and the circuit is still low, replace the driver module.

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