P25A4Fuel Mode Select Switch Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P25A4 is the general circuit fault for the fuel mode select switch – the button on bi-fuel vehicles with which the driver chooses between gasoline and an alternative fuel such as CNG or LPG. GM's 2015 bi-fuel Impala, described in PI1330, has it on the instrument panel left of the steering wheel; on the 2016 Silverado and Sierra 2500HD CNG trucks it sits in the centre stack and carries the fuel indicator. The engine module reads the switch line and logs P25A4 when it finds no valid signal at all, typically an open wire, a loose connector or a dead switch. No manufacturer documents P25A4 publicly. P25A5 covers plausibility, P25A6 and P25A7 low and high levels, P25A8 dropouts. The engine usually stays on gasoline or on the last mode, and switching by hand no longer works.
- What you may notice
- Fuel cannot be changed with the switch
- Engine runs on gasoline only
- Fuel indicator light on the switch dark or flashing
- Likely causes
- LikelyOpen wire or unplugged connector at the fuel mode switch
- PossibleFuel mode switch failed internally
- PossibleFaulty connection in a bi-fuel conversion harness
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €30 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.