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DTC codes / Ford codes / P1237

P1237 · FordFuel Pump Secondary Circuit Fault

P1237 on Ford vehicles indicates that the powertrain control module (PCM) has detected an abnormal condition in the secondary circuit of the fuel pump, which is the monitoring or feedback path separate from the main power feed to the pump. The PCM compares expected voltage or current on this circuit against actual values and sets the code when the signal falls outside the programmed range, often due to a wiring fault, a failing fuel pump driver module, or a problem inside the fuel pump assembly itself.

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

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • Engine cranks but fails to start or starts only after prolonged cranking
  • Intermittent stalling or a sudden loss of power while driving
  • Rough running or hesitation under acceleration due to inconsistent fuel delivery
  • A faint whine or unusual noise from the fuel tank area when the key is turned on

Common causes, most likely first

  1. Damaged or corroded wiring in the fuel pump secondary circuit, especially at connectors or where the harness passes near the fuel tank
  2. Faulty fuel pump driver module (FPDM) on vehicles so equipped, which controls pump speed and reports circuit status
  3. Internal fault in the fuel pump assembly, such as a failed fuel level sensor or pump motor winding that affects the secondary signal
  4. Blown fuse or faulty relay in the fuel pump circuit that interrupts the secondary monitoring path
  5. Poor ground connection for the fuel pump or FPDM, causing voltage drops that mimic a circuit fault
  6. Corrosion or water intrusion in the fuel pump electrical connector at the tank

How to diagnose and fix it

  1. Retrieve all stored and pending codes with a scan tool to confirm P1237 is the only fuel-related code and check for related codes like P0230 or P0231
  2. Inspect the fuel pump fuse and relay, and test the relay operation with a known-good substitute or a multimeter
  3. Visually inspect the fuel pump wiring harness and connector at the tank for chafing, corrosion, or loose pins, repairing as needed
  4. Measure voltage and resistance on the secondary circuit at the fuel pump connector and compare with factory specifications
  5. Test the fuel pump driver module (if equipped) by checking its power, ground, and signal outputs with a multimeter or oscilloscope
  6. Perform a fuel pressure and volume test to rule out a mechanical pump failure that could affect the secondary circuit feedback
  7. If all external circuits test good, replace the fuel pump assembly or FPDM as indicated by the diagnostic results

What Ford techs check before replacing the pump

  • A loose or corroded ground strap at the fuel tank can cause P1237 without any fault in the pump itself, so always verify ground integrity before condemning parts.
  • On Ford vehicles with a fuel pump driver module, the module often fails due to water intrusion or heat, and it can set P1237 even when the pump is healthy.
  • The secondary circuit is not the main power feed; technicians who only check for 12 volts at the pump may miss a faulty feedback wire that triggers this code.
  • Intermittent P1237 codes are frequently caused by a chafed wire near the fuel tank that only shorts when the suspension compresses or the tank is full.
  • A failing fuel level sensor inside the pump assembly can affect the secondary circuit signal on some Ford models, so check live data for fuel level rationality.

Can I keep driving with P1237?

You can usually drive short distances to a repair shop if the engine runs normally, but avoid heavy acceleration, towing, or long trips because an intermittent fuel pump fault can cause sudden stalling. If the engine cranks but does not start or stalls repeatedly, stop driving and arrange a tow to prevent a dangerous breakdown.

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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