Wiring fault in the pump secondary circuit (chafed, corroded or open-circuit wire, or short to earth or supply); Corroded, loose or heat-damaged connector or terminals at the pump, relay or control module; Faulty fuel pump relay or its socket; Failing fuel pump or secondary pump drawing abnormal current; Blown fuse or poor power or earth supply to the pump circuit; Faulty fuel pump driver or control module, where fitted; Fault inside the engine control unit.

P1237

Fuel Pump Secondary Circuit Malfunction.

Other
Powertrain
Manufacturer code
Medium severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
2: AreaFuel and air metering (injector circuit)
37: FaultThe specific fault in that area

What it means

P1237 is a manufacturer-specific code that, for the definition supplied here, means a fault in the fuel pump secondary circuit. The engine control unit monitors the pump's secondary control or power circuit (relay, driver module or second pump, depending on the model) and found a voltage or current reading that did not match what it commanded. The exact circuit layout varies by model and engine, and other makes use P1237 for unrelated faults such as an injector circuit, so confirm the make-specific definition first.

Symptoms

Engine cranks but is long to start or does not start
Engine stalling or cutting out, especially under load or when hot
Hesitation or loss of power under acceleration
Engine warning light on
Fuel pump not audibly priming when the ignition is switched on
Intermittent fault that comes and goes

Possible causes

Wiring fault in the pump secondary circuit (chafed, corroded or open-circuit wire, or short to earth or supply)likely
Corroded, loose or heat-damaged connector or terminals at the pump, relay or control modulelikely
Faulty fuel pump relay or its socketlikely
Failing fuel pump or secondary pump drawing abnormal currentpossible
Blown fuse or poor power or earth supply to the pump circuitpossible
Faulty fuel pump driver or control module, where fittedrare
Fault inside the engine control unitrare

How to diagnose

Confirm the make and model, and look up the manufacturer's definition and circuit layout for P1237 on that vehicle.
Read all stored codes and freeze frame data, noting whether the fault is current or historic and any related fuel pressure or power supply codes.
Check the relevant fuses and the fuel pump relay, and look for heat marks or corrosion in the sockets.
Inspect the wiring and connectors along the pump circuit, including the connector at the fuel tank, looking for chafing, water ingress and green corrosion.
Listen for the pump priming with the ignition on, and wiggle the harness while monitoring live data for the fault returning.
Measure supply voltage and earth integrity at the pump connector with the circuit commanded on, using the wiring diagram.
Check pump current draw and fuel pressure against the manufacturer's specification.
Test the relay and driver module output, and only then suspect the control unit.

How to fix

Repair or replace damaged wiring and restore the correct circuit insulation and routing.
Clean, repair or replace corroded or damaged connectors and terminals.
Replace a faulty fuel pump relay or a damaged relay socket.
Replace the fuel pump or secondary pump if its current draw or pressure is out of specification.
Replace a blown fuse only after finding and fixing the cause of the overload.
Replace or reprogram a faulty pump driver module or control unit as a last resort, once the rest of the circuit is proven good.

Can I keep driving?

Medium severity

The car may run, but a fuel pump fault can cause stalling or a no-start without warning, which is a safety risk in traffic. Avoid long journeys and get it diagnosed soon.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.