P0231 Fuel Pump Secondary Circuit Low

P0231 indicates low voltage in the fuel pump secondary circuit. The monitored pump output circuit is lower than expected under command.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace the pump before checking voltage drop and ground; low circuit voltage can make a good pump underperform.

Symptoms of P0231

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0231

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Check fuel pump relay output, pump power feed, ground, connector condition, voltage drop, and wiring near the tank.
Compare commanded pump state with actual fuel pressure and voltage at the pump under load.
Inspect fuse links, relay contacts, fuel pump module connectors, and harness areas exposed to corrosion.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.