P0231 — Fuel Pump Secondary Circuit Low

Does P0231 always mean the fuel pump is defective?

No. P0231 identifies a low condition in the secondary fuel-pump control circuit, and the relay, fuse, wiring, connector, ground, pump, or control module may be responsible.

Can I safely drive with P0231 stored?

Only with caution. If fuel pressure is stable and the engine does not stall, a short trip may be possible, but a failed secondary pump can cause an abrupt loss of power and should be repaired promptly.

What should an OBD-II scanner show for P0231?

A generic ELM327 or AIScanAuto scan should confirm the code and related freeze-frame information. Live pump-command or feedback data may also reveal a commanded pump that is not responding, although data availability varies by vehicle.

Why might P0231 return after replacing the fuel-pump relay?

The relay may not be the faulty component, or the problem may remain in the wiring, connector, ground, fuse feed, or control module. The old code must also be cleared and the repair verified under operating conditions.

The engine control module logs code P0231 when it detects that the fuel pump secondary circuit is running at a voltage lower than it should be. In plain language, P0231 means the fuel pump secondary circuit is stuck near ground — the signal isn't getting the voltage it needs to do its job. This falls under the powertrain category of OBD2 codes, which covers engine and transmission management systems.

When the secondary circuit voltage drops below the minimum threshold, the module interprets this as a problem somewhere in the fuel delivery wiring or the pump itself. The culprits are usually a wire with damaged insulation shorting to metal, a connector that's corroded or loose, a supply line that's lost power, or a fuel pump that's failing and pulling the circuit down. The key point is that P0231 won't set on a single bad reading — the fault must repeat under specific conditions (engine load, temperature, speed) before the check engine light comes on. That freeze frame data is valuable because it shows exactly what was happening when the problem appeared.

When the module logs P0231, it also captures freeze frame data — a snapshot of engine load, RPM, coolant temperature, and vehicle speed at the moment the fault occurred. Reproducing those exact conditions during your road test gives you the best chance of triggering the problem while you're diagnosing it.

Symptoms of P0231

• Noticeable loss of power when the engine is under load
• Fuel odor, especially if the problem is advanced
• Fuel economy dropping below normal
• Check engine light illuminated on the dashboard
• Engine cranks longer than normal before starting
• Rough idle and hesitation during acceleration

What causes P0231?

• Fuel pump failure causing the secondary circuit to pull low
• No voltage reaching the fuel pump secondary circuit
• Signal wire shorted to ground from chafed or melted insulation
• Fuel contamination or the wrong fuel grade in the tank
• Fuel pressure regulator not maintaining correct rail pressure
• Vacuum leaks or intake manifold faults skewing the air-fuel mixture
• Failed fuel rail pressure sensor or damaged wiring to the sensor
• Clogged or leaking fuel injectors disrupting delivery to cylinders
• Weak fuel pump output or a clogged fuel filter restricting flow

How to diagnose P0231

1. Plug in an OBD2 scanner, verify that P0231 is stored in the ECM memory, and record all freeze frame data. This tells you engine conditions when the fault first appeared.
2. Look for any other stored trouble codes — related faults often point to the real root cause. Also check manufacturer TSBs for your specific make and model; many common OBD2 problems have factory service bulletins or software updates that address them. Search by your VIN on the manufacturer website or nhtsa.gov.
3. Inspect the wiring harness and connectors tied to the fuel pump and pressure regulation system. Look for damaged wire insulation, corrosion at connectors, broken locks, or wires touching hot engine components.
4. Check for proper supply voltage at the fuel pump secondary connector first. Then measure resistance from the signal wire to chassis ground — a reading near zero ohms confirms a short to ground in the harness.
5. Measure fuel pressure at the rail with a gauge and compare it against factory specifications, both at idle and under load.
6. Review short-term and long-term fuel trims in the scanner's live data stream. Sustained high or low trims indicate whether the mixture is running rich or lean.
7. Clear the code, drive through a complete drive cycle including the specific conditions from the freeze frame, and verify that P0231 does not return.

Repair options and costs

Address the most common and affordable causes before replacing major components:

• Replace the fuel pump: $400–$900
• Replace the fuel pressure regulator or sensor: $150–$450
• Clean or replace fuel injectors: $200–$800
• Replace the fuel filter: $80–$200

Total repair cost for P0231

The final bill depends entirely on which part is actually faulty. At independent shop rates (parts and labor, USD), common repair scenarios for P0231 break down as follows: fuel pump replacement runs $400–$900, pressure regulator or sensor replacement costs $150–$450, injector cleaning or replacement ranges $200–$800, and fuel filter replacement runs $80–$200. Most P0231 repairs end up between $80 and $900 total. Getting an accurate diagnosis before buying parts is the smartest move — the most expensive fix is rarely the first thing to check.

Can you drive with P0231?

Drive with caution. A fuel delivery or mixture control issue can cause the engine to stall, hesitate in traffic, or misfire. In severe cases, an overly rich mixture can damage the catalytic converter over time. Avoid long highway trips until the fault is diagnosed and repaired.

Related OBD2 codes

• P0200: Injector Circuit Malfunction
• P0201: Injector Circuit Malfunction - Cylinder 1
• P0202: Injector Circuit Malfunction - Cylinder 2
• P0203: Injector Circuit Malfunction - Cylinder 3
• P0204: Injector Circuit Malfunction - Cylinder 4
• P0205: Injector Circuit Malfunction - Cylinder 5