P0231 Code: Fuel Pump Secondary Circuit Low

What the P0231 code means

The computer turns the fuel pump on through a relay or a fuel pump control module. When you turn the key on it runs the pump for a few seconds to pressurize the system and then keeps it on while the engine is turning. On many modern vehicles it also regulates the pump speed according to demand.

The P0231 code means the voltage in the control circuit is lower than expected: normally a short to ground or no supply. The computer watches the voltage at its own control transistor (the driver): when the component is off it expects to see supply voltage and, when it turns it on, a drop to almost zero. Any other combination tells it there is an open circuit or a short.

The pump is one of the most demanding electrical loads on the vehicle: a connector with high resistance heats up, melts and cuts the voltage reaching the pump, which then spins slower and delivers less flow. That is why many faults that look like a bad pump are really a problem with its connector, its ground or its relay.

Always check the wiring and the power supply before you replace the component: they are the most common cause and the cheapest.

P0231 code symptoms

• Check engine light on.
• Hard starting, jerking or an engine that stalls.
• The engine cranks but does not start.
• Loss of power under load.
• The pump cannot be heard when the key is turned on.

Likely causes of the P0231 code

1. Control wire shorted to ground: the component stays on permanently or the driver protects itself.
2. Supply interrupted: blown fuse, defective relay or a cut supply wire.
3. Component shorted inside: its resistance is much lower than specified.
4. Connector with moisture or corrosion that creates a path to ground.

How to diagnose the P0231 code step by step

1. Command the component with the scan tool and check whether it responds (click, hum, movement or pressure).
2. Check the fuse and relay: measure voltage on both sides of the fuse; swap the relay with an identical one to test.
3. Measure the supply at the connector: there should be battery voltage with the key on (or during activation).
4. Measure the component resistance and compare it with the manual; also check the insulation to ground (infinite).
5. Check the control wire: continuity to the computer (less than 1 ohm) and no short to ground or to 12 V.
6. Listen for the pump when you turn the key on. It should run for 2 to 3 seconds.
7. Measure the fuel pressure at idle and under load.

How to fix the P0231 code

• Repair the connector, the wiring or the power supply.
• Replace the fuel pump if it does not respond with correct power and control.
• Clear the codes and verify on the road.

Technical reference data

• Pump supply: 12 V through a relay or module (sometimes with PWM control).
• Typical pump current draw: 4 to 8 A.
• Typical pressure: 3 to 4 bar (about 44 to 58 psi) on port injection; 4 to 6 bar (about 58 to 87 psi) of low pressure on direct injection.
• Approximate values only: check the manufacturer data for your engine.

Brand-specific notes

Check the pump connector on top of the tank: the heat from a bad contact often melts it.

Frequently asked questions about P0231