If the fuel pump gets weak power, fuel pressure drops, and the engine stumbles, loses power or will not start. A P0231 code means the engine computer saw low voltage on the fuel pump secondary circuit, the power side that runs the pump.
This guide explains what pulls the pump voltage low, how to test it and how to avoid replacing a good pump.
P0231 Code Breakdown
Every OBD-II code follows the same five-character pattern set by the SAE J2012 standard. Each character narrows down which system has the fault. This table shows what each part of the code tells you.
| Character | Meaning | What It Tells You |
|---|---|---|
| P | Powertrain | The fault is in the engine or transmission systems. |
| 0 | Generic (SAE) code | The definition is the same on every OBD-II vehicle. |
| 2 | Fuel and air metering | The fault involves fuel and air metering, such as injectors, the fuel pump, throttle sensors or boost control. |
| 31 | Specific fault | Fuel Pump Secondary Circuit Low |
What the P0231 Code Means
The SAE J2012 standard defines the P0231 code as Fuel Pump Secondary Circuit Low. Most fuel pumps are powered through a relay. The powertrain control module (PCM) switches the relay coil, which is the primary or control side of the circuit. The relay contacts then send battery power to the pump, which is the secondary or power side.
Many Ford, Lincoln and some other vehicles use a fuel pump driver module (FPDM) instead of a simple relay. The PCM tells the module how fast to run the pump, and the module powers it. On these vehicles, the module is often mounted on the frame or near the spare tire, where it is exposed to water and road salt.
The PCM watches the circuit it controls and, on many vehicles, a feedback wire from the pump side. When those voltages do not match its command, it sets a fuel pump circuit code.
This code points to the secondary side. The PCM commanded the pump on, but the feedback voltage on the pump side stayed low. That usually means power is not reaching the pump circuit, or the pump is drawing it down.
Symptoms of Low Fuel Pump Voltage
Fuel delivery problems are hard to miss. Common signs of a P0231 code include:
- Engine cranks but will not start
- Hesitation or loss of power under load
- Stalling, especially when hot
- Fuel pump that runs louder or slower than normal
- Check engine light on
A pump that is starting to fail often works at idle but cannot keep up under load, when the engine needs the most fuel.
What Causes the P0231 Code?
These are the usual causes on the power side:
- Blown fuel pump fuse. Often caused by a pump that is drawing too much current.
- Worn relay contacts. Burnt contacts drop voltage to the pump.
- Open or corroded wiring. Especially at the connector on top of the tank.
- Tripped inertia switch. Common on older Fords after a jolt.
- Failing fuel pump. A worn pump motor can pull the voltage down.
- Bad pump ground. Corroded grounds near the tank add resistance.
Tools You Will Need
You can do most of this testing at home with basic tools:
- OBD-II scan tool that can command the fuel pump
- Digital multimeter and test light
- Fuel pressure gauge for your fuel system
- Fused jumper wire
- Wiring diagram showing the relay or fuel pump driver module
Step-By-Step Diagnosis of the P0231 Code
Fuel pump circuits are simple, so a careful step-by-step check usually finds the fault quickly. Keep sparks and flames away from the fuel system while you test.
Check the Fuse and Inertia Switch
Check the fuel pump fuse and reset the inertia switch if your vehicle has one. A fuse that blows again right away points to a short or a pump drawing too much current.
Measure Voltage at the Pump
Command the pump on and measure voltage at the pump connector, usually on top of the tank. It should be within about 1 volt of battery voltage. Then measure the pump ground to the battery negative post, which should be under 0.1 volt.
A big drop means resistance in the relay, wiring or connectors, which you can find by measuring voltage drop across each section.
Check Fuel Pressure
Connect a fuel pressure gauge and compare it with the specification. Many port injection systems run about 40 to 60 psi. Low pressure with good voltage at the pump points to a weak pump or clogged filter.
Check Pump Current
If you have a clamp-on amp meter, measure pump current. A typical pump draws about 4 to 8 amps. Much higher current means the pump is binding, and lower current with good voltage can mean a worn motor.
Repairs That Clear the P0231 Code
Match the repair to what your tests found. Then clear the code and drive under the same conditions that set it.
- Replace a blown fuse and find out why it blew.
- Replace the relay if its contacts drop voltage.
- Repair corroded wiring and the connector on top of the tank.
- Clean pump grounds
- Replace the fuel pump if it draws too much current or cannot make pressure with good voltage.
The connector on top of the fuel tank often melts when its pins get loose. If you replace the pump, check that connector and replace the pigtail if it is discolored.
Common Mistakes to Avoid
These mistakes waste money or leave the real fault in place:
- Replacing the fuel pump before checking the relay, fuse and driver module
- Forgetting the inertia switch on vehicles that have one
- Jumping the relay socket with an unfused wire
- Ignoring corrosion on a frame-mounted fuel pump driver module
Typical Repair Costs
The cost to fix a P0231 code depends on the cause. This table shows typical ranges for parts and labor.
| Repair | DIY Cost | Typical Shop Cost |
|---|---|---|
| Fuse or relay | $5 to $40 | $50 to $150 |
| Wiring or connector repair | $10 to $50 | $100 to $350 |
| Fuel pump driver module | $60 to $250 | $200 to $500 |
| Fuel pump assembly | $100 to $500 | $400 to $1,200 |
Fuel pump replacement is the most expensive repair here, especially on vehicles where the tank must be dropped. A relay, fuse or driver module is far cheaper and causes many of these codes, so test them first.
Is It Safe to Keep Driving with a P0231 Code?
It is risky. A fuel pump circuit fault can cut fuel without warning and stall the engine, which can leave you stranded or stopped in traffic.
If the engine runs normally, drive only as far as needed to reach a repair. If it stalls, cranks without starting or loses power, have it towed.
Related Codes
These codes often show up with this one or point to the same system:
| Code | Meaning |
|---|---|
| P0230 | Fuel Pump Primary Circuit Malfunction |
| P0232 | Fuel Pump Secondary Circuit High |
| P0233 | Fuel Pump Secondary Circuit Intermittent |
| P0087 | Fuel Rail/System Pressure Too Low |
| P0627 | Fuel Pump A Control Circuit/Open |
Restoring Full Power to the Fuel Pump
A P0231 code means the fuel pump power circuit has low voltage. Blown fuses, worn relays, corroded wiring and failing pumps cause most cases.
- Check the fuse and inertia switch.
- Measure voltage and ground at the pump.
- Test fuel pressure.
- Replace the pump only if it fails with good voltage.
Frequently Asked Questions
Can a Bad Fuel Pump Cause the P0231 Code?
Yes. A worn pump motor can draw too much current, which drops voltage on the circuit and can blow the fuse. But wiring and relay faults cause the same code, so measure voltage at the pump before you replace it.
Where Is the Fuel Pump Relay?
Most vehicles keep it in the underhood fuse and relay box, and the lid or owner’s manual shows its position. Vehicles with a fuel pump driver module often mount the module on the frame rail, near the spare tire or behind a trim panel in the trunk.
What Is an Inertia Switch?
Some vehicles, especially older Fords, have an inertia switch that cuts fuel pump power after a hard jolt or crash. A bump or pothole can trip it too. It is often in the passenger footwell or trunk, and pressing its reset button restores power.
How Long Does a Fuel Pump Last?
Many fuel pumps last 100,000 miles or more. Running the tank low often, contaminated fuel and a clogged filter shorten their life. A pump that is getting louder, or an engine that loses power on hills, can be early signs of wear.
Can a Weak Battery Cause Fuel Pump Codes?
It can. Low system voltage makes the pump run slower and can drop the feedback voltage the PCM reads. Test the battery and charging system, and clean the battery terminals, before you replace fuel pump parts.