Can you keep driving?
Can you keep driving?
Stop driving if any of these apply
- !The engine starts stalling, losing power sharply, or refusing to respond to throttle normally.
- !The check-engine light flashes or the vehicle suddenly runs much worse after the code appears.
What to check first
Step-by-step checks
- 1
Free - no tools
Check whether the fuel pump primes normally at key-on and whether the engine stalls under load
- 2
Free - no tools
Inspect the relay, fuse, and pump connector for heat damage, corrosion, or looseness
- 3
Basic tool needed
If the vehicle has a fuel pump module or controller, check that side of the circuit too
- 4
Basic tool needed
If scan data is available, compare commanded fuel pressure or pump activity with actual behavior
- 5
Basic tool needed
Avoid replacing the pump until the electrical side has been checked carefully
If the code returns
- -If direct power makes the pump run correctly, the pump may be fine and the control side becomes more likely.
- -If the voltage drop is on the feed side, relay or wiring repair comes before a pump.
- -If the code returns after a repair, recheck the connector fit and ground side again.
Background
What this code means
P0231 is a generic OBD-II code for a low-input fuel pump secondary circuit fault.
That typically means the pump or the circuit feeding it is not seeing enough voltage or current to behave normally.
Diagnosis
Common causes
Voltage drop in the pump circuit
Low circuit voltage can cause the secondary side to read below expected levels.
Weak relay output
A relay that still clicks may not deliver enough current.
Connector or harness issue
A corroded or loose connection can reduce the pump-side reading.
Pump module fault
The pump or module may be weak even if the control side looks fine.
Avoid these mistakes
What not to do
- xDo not replace the sensor or pump first if there is obvious wiring, connector, or intake damage.
- xDo not ignore drivability changes or stalling just because the code sounds electrical.
Parts
Parts that may need replacing
See also
Related OBD codes
Source notes
Generic OBD-II (SAE J1979 / ISO 15031-5). P0231 was expanded around common low-input fuel-pump secondary circuit faults, especially voltage drop, relay issues, and connector damage.
This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.
This is generic OBD-II guidance and should not override vehicle-specific service information. Exact diagnosis and repair steps vary by make, engine family, and model year.
Last reviewed: 2026-04-10
Reference: Open reference