Faulty fuel pump relay or relay contacts; Wiring fault in the pump feed or earth, such as a chafed, shorted or corroded wire; Corroded, loose or water-damaged connector at the relay, fuse box, pump or tank; Worn fuel pump drawing excess current and pulling the circuit voltage down; Blown or high-resistance fuse or poor power supply to the circuit; Faulty fuel pump driver or control module, where fitted.

P0231

Fuel Pump Secondary Circuit Low.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
2: AreaFuel and air metering (injector circuit)
31: FaultThe specific fault in that area

What it means

P0231 is the generic code for a low signal in the fuel pump secondary circuit. The secondary circuit is usually the feed that powers the pump, often switched by a relay or pump control module, and it is separate from the primary control circuit. The engine control unit saw the voltage in that circuit lower than expected, for example when the pump should be running or when the circuit is being monitored. The exact circuit layout varies by model and engine.

Symptoms

Engine cranks but is long to start or does not start
Engine stalls shortly after starting or while driving
Loss of power or hesitation under load
Fuel pump not heard priming when the ignition is switched on
Engine warning light on, possibly with other fuel pressure or fuel trim codes

Possible causes

Faulty fuel pump relay or relay contactslikely
Wiring fault in the pump feed or earth, such as a chafed, shorted or corroded wirelikely
Corroded, loose or water-damaged connector at the relay, fuse box, pump or tanklikely
Worn fuel pump drawing excess current and pulling the circuit voltage downpossible
Blown or high-resistance fuse or poor power supply to the circuitpossible
Faulty fuel pump driver or control module, where fittedrare

How to diagnose

Read the stored codes and freeze frame data, noting any other fuel pressure, fuel trim or relay codes and the conditions when the fault set
Listen for the fuel pump priming when the ignition is switched on and check the relevant fuse
Inspect the wiring, relay socket and connectors for damage, heat marks, corrosion or water ingress, including at the pump and in the boot or under the rear seat where applicable
Check the fuel pump relay by swapping it with a known good identical one or testing it, following the manufacturer's procedure
With a multimeter, check the supply voltage and earth integrity at the relay and the pump connector with the pump commanded on, comparing against the wiring diagram
Voltage-drop test the feed and earth circuits under load to find high resistance
Measure pump current draw and fuel pressure against the manufacturer's specification to judge pump condition
If the circuit tests good, check the pump driver or control module power, earth and command signal as specified for that model

How to fix

Replace a faulty fuel pump relay
Repair or replace damaged wiring, and clean or renew corroded terminals and connectors
Replace the fuse after finding and correcting the cause of any overload
Replace a worn or high-current fuel pump if testing confirms it is at fault
Repair the power or earth supply fault found during voltage-drop testing
Replace or repair the pump control module only after the circuit and pump are proven good

Can I keep driving?

High severity

Avoid driving until it is diagnosed, as the engine may stall without warning, which is unsafe in traffic. If the car starts and runs normally, limit driving to getting it to a workshop.

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