What it means
The voltage on the secondary side of the fuel pump circuit is below the expected level when the pump is commanded on. Often caused by a failed pump motor, corroded ground, or wiring fault.
At a glance
- Usually lights the check-engine light
How it works
The fuel-pump secondary circuit carries power through to the pump motor and its ground when the pump is commanded on. P0231 sets when the monitored secondary-side voltage is below the expected level, which can result from a worn pump motor, a poor ground, or resistance in the connector or wiring.
Common causes
Most likely first.
- Fuel pump motor failed or worn
- Pump ground point corroded
- Connector pins corroded - high contact resistance
Symptoms
- Check engine light on
- Hard start, no start, or stalling under load
- Power loss especially at high load or rpm
- Possible long cranking time
How to diagnose it
- Record freeze-frame data and check for related fuel-pump codes to see whether low voltage occurred during cranking, idle, or engine load.
- Inspect the pump connector, accessible wiring, and ground point for corrosion, looseness, damage, or signs of heating.
- With the pump commanded on, measure voltage on the secondary side and compare it with the vehicle's wiring diagram and manufacturer's specification.
- Check voltage drop across the pump ground and power connections while the pump is operating to find resistance that a visual check may miss.
- If the wiring and ground meet specification but voltage remains low, test the pump motor and fuel delivery before replacing the pump.
Common fixes
- Clean and secure the fuel-pump ground connection.
- Repair corroded or high-resistance pump connector terminals.
- Repair damaged secondary-circuit power or ground wiring.
- Replace a worn fuel-pump motor if testing confirms it is responsible for the low circuit voltage.
Can I keep driving?
Low pump-circuit voltage can cause long cranking, loss of power under load, or stalling, so avoid high-speed driving and situations where a stall would be dangerous. If the engine begins to stall or will not restart, stop safely and arrange assistance.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.