P0231

Fuel Pump Secondary Circuit Low

P0231 is a generic OBD-II powertrain diagnostic trouble code: Fuel Pump Secondary Circuit Low. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0231
Group
Powertrain
System
Powertrain
Severity
Critical (limp mode / no-start)
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What P0231 means

P0231 — Fuel Pump Secondary Circuit Low — means the ECU has commanded the fuel pump relay closed but is reading lower voltage than expected on the pump's supply (feedback) wire. Many PCMs splice a monitoring wire into the feed between the relay output and the pump connector; this lets the ECU confirm that voltage is actually reaching the pump after the relay energises. When that monitored voltage is below threshold, P0231 is stored.

The fault sits on the output side of the relay: the pump connector, the pump motor windings, the wiring between the relay and the pump, or an open fuse in that leg. A completely dead pump draws no current and collapses the feedback voltage to near zero, which is the most common trigger. A failed FPCM (Fuel Pump Control Module, present on some platforms to enable variable pump speed) can also produce this fault by failing to pass voltage through to the pump.

The consequence is the same as any fuel delivery failure — hard start, stall, or no-start — but because the relay is energising correctly, the diagnosis pivots away from the relay and toward the pump, its fuse, the harness, and on some vehicles the FPCM.

Common causes

Most-frequently reported root causes when P0231 is logged.

  • 1
    Failed in-tank fuel pump motor drawing no current and pulling the supply line low.
  • 2
    Blown fuel pump secondary fuse or fusible link between the relay output and the pump.
  • 3
    Open circuit in the wiring harness between the relay output and the pump connector.
  • 4
    Corroded or loose pump connector causing high resistance that drops voltage below the PCM threshold.
  • 5
    Faulty Fuel Pump Control Module (FPCM) on vehicles equipped with variable-speed pump management.
  • 6
    Failed PCM feedback circuit — the internal monitoring input is damaged or reads incorrectly.
  • 7
    Intermittent contact in the pump wiring due to chafing against the fuel tank or chassis.

Symptoms drivers notice

Engine fails to start or requires extended cranking before it fires.
Engine stalls shortly after starting, especially under any load.
Hesitation and stumble during acceleration as fuel pressure cannot be maintained.
Check Engine Light illuminated; P0231 stored in PCM memory.
No audible fuel pump hum during the key-on priming cycle.
Fuel pressure gauge shows zero or well below specification during cranking.

How to diagnose P0231

A typical diagnostic flow when this code is present.

  1. 1
    Scan for all DTCs; note whether P0230 (primary circuit) is also present — if both are set, start at the relay and fuse.
  2. 2
    With ignition ON, listen at the fuel tank for the pump priming hum; absence suggests the pump or its supply is open.
  3. 3
    Check the fuel pump secondary fuse and any fusible link downstream of the relay for continuity.
  4. 4
    Back-probe the pump connector with a multimeter while commanding the pump on — expect battery voltage; a low or zero reading confirms an open on the supply side.
  5. 5
    Inspect the wiring harness for damage, particularly where it routes near the tank edge or chassis.
  6. 6
    On FPCM-equipped vehicles, check FPCM supply voltage and ground before condemning the pump.
  7. 7
    Measure fuel pressure at the rail during cranking; zero pressure with correct voltage at the connector points directly to a failed pump motor.

Related powertrain codes

Frequently asked questions

Is P0231 always a failed pump?

Not always. A blown secondary fuse or open wiring harness can set P0231 with a perfectly healthy pump. Always verify voltage is reaching the pump connector before replacing the pump.

What is the 'secondary circuit' in P0231?

The secondary circuit is the voltage-supply wire on the output side of the fuel pump relay — from the relay through to the pump. The PCM monitors this wire via a feedback tap; 'low' means that monitored voltage is below the expected operating level.

Can a bad ground cause P0231?

Yes. A high-resistance or open pump ground causes the supply voltage to collapse even if the relay and wiring are intact. Always check the pump ground at the tank as part of diagnosis.

How urgent is repair?

Very urgent. The engine will stall or not start reliably. Continued cranking attempts with no fuel delivery also stress the starter motor and battery.

Disabling P0231 in software

RaceTune can permanently disable P0231 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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