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DTC codes / Ford codes / P1231

P1231 · FordHigh Speed Fuel Pump Relay Activated

P1231 on Ford vehicles means the powertrain control module has commanded the high-speed fuel pump relay on, but the circuit feedback indicates the relay is still activated when it should not be. The computer detects an unexpected voltage on the relay control circuit that suggests the relay coil or driver is stuck on, which can cause the fuel pump to run continuously and flood the engine or drain the battery.

SystemPowertrain
Code typeFord specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering (injector circuits)

Symptoms you may notice

  • Often no symptoms besides the warning light, especially if the relay only sticks intermittently
  • Extended cranking or a flooded engine after sitting, because the pump runs when it should be off
  • Strong fuel odor from the tailpipe or engine bay due to excess fuel delivery
  • Battery drain or a dead battery overnight if the relay remains energized with the key off
  • Rough idle or black smoke from the exhaust as the engine runs rich
  • Fuel pump running audibly with the key off or after the engine is shut down

Common causes, most likely first

  1. High-speed fuel pump relay coil internally shorted or stuck closed
  2. Short to power in the relay control wire between the powertrain control module and the relay
  3. Faulty powertrain control module driver holding the relay ground circuit active
  4. Corroded or damaged relay socket terminals causing unintended contact
  5. Aftermarket alarm or remote start wiring tapped into the fuel pump circuit
  6. Water intrusion into the relay box or fuse panel causing a short

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related fuel pump or relay codes before touching parts
  2. Listen for the fuel pump running with the key off and confirm the relay is energized when it should not be
  3. Swap the high-speed fuel pump relay with an identical known-good relay from the same fuse box and clear the code
  4. Inspect the relay socket and wiring for corrosion, chafing, or signs of a short to power
  5. Measure voltage on the relay control circuit at the powertrain control module connector with the key off to check for a short
  6. Disconnect the powertrain control module and check whether the relay remains energized, which isolates a wiring short from a module fault
  7. Repair or replace the faulty wiring, relay, or powertrain control module as indicated by the tests, then clear and recheck the code

When the relay is not the real culprit

  • A short to power in the relay control wire is more common than a failed powertrain control module, so always ohm-test the wire before condemning the module.
  • Aftermarket remote start or alarm systems spliced into the fuel pump circuit frequently cause this code by backfeeding voltage onto the relay control wire.
  • The code can set intermittently from a relay that sticks only when hot, so a cold relay that tests fine does not rule out the relay as the cause.
  • A weak battery or poor ground can cause the powertrain control module to misread the relay feedback circuit, so check charging system health first.
  • Replacing the relay without checking the control wire often leads to a repeat failure when the underlying short remains.

Can I keep driving with P1231?

You can drive short distances to a repair shop, but avoid leaving the vehicle parked for long periods because a stuck relay can drain the battery or flood the engine. If you smell raw fuel or see the fuel pump running with the key off, stop driving and have it repaired immediately.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Ford vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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