P0231: Fuel Pump Secondary Circuit Low
The voltage in the circuit that feeds the fuel pump is lower than expected.
High risk
The engine may stall or not start. Have it checked soon.
Short answer · Can I keep driving with P0231?
With caution. If the pump supply drops while driving, the engine can stop. If the car does not start, have it towed.
What does P0231 mean?
P0231 means the engine control unit monitors the supply side of the fuel pump, between the relay and the pump, and sees too little voltage there. A failed relay, a blown fuse, a broken or corroded wire, a poor ground or a failing pump that draws too much current are typical causes.
What the car does when the code is set
The check engine light comes on and many engines limit power to protect themselves. The car may hesitate under acceleration, misfire or stall, especially under load, and it may be hard to restart.
How the system works
A low-pressure pump in the tank supplies fuel to the engine. On port-injection petrol engines that pressure feeds the injectors directly. On diesels and direct-injection petrol engines, a mechanical high-pressure pump raises it much further, into a common rail that feeds all the injectors. A pressure sensor on the rail tells the engine control unit the actual pressure, and a regulator or metering valve adjusts it to the target. If the measured pressure stays below the target for too long, the control unit stores a low-pressure code and may limit power.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Faulty fuel pump relayThe relay output that feeds the pump has failed or its contacts are burnt.
- Clogged fuel filterRestricts flow, especially under load.
- Weak fuel pumpThe in-tank pump or high-pressure pump cannot keep up.
- Faulty pressure sensor or regulatorThe pressure is measured or controlled incorrectly.
- Air in the fuel system or running low on fuelCommon on diesels after running the tank dry or after a filter change.
- Fuel leakAn external leak lowers the pressure.
How it is diagnosed
- Check fuel level and leaksMake sure there is enough fuel and look for wet spots or fuel smell under the car and in the engine bay.
- Compare desired and actual pressureLive data shows the target and measured rail pressure. A gap under load points to supply problems.
- Check the filter and low-pressure supplyReplace an old filter and measure the feed pressure from the tank pump.
- Test the pressure sensorCompare the sensor reading with a mechanical gauge where possible.High-pressure fuel systems can hold pressure after switching off. Only a trained technician should open them.
Questions about P0231
Is the pump itself faulty with P0231?
Sometimes. A pump that draws too much current can pull the voltage down, but wiring and the relay are more common causes. Check them first.
Why does the engine lose power only under load?
Under load the engine needs the most fuel. A weak pump or clogged filter can keep up at idle but not under full load.
Can I drive until the next service?
Not recommended. The engine may stall in traffic. Have the fuel filter and pressure checked soon.