P25A4 code meaning
Fuel Mode Select Switch Circuit
Powertrain system Generic code P25xx codes Check engine light
What P25A4 means
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.
P25A4 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P25A4
- Fuel cannot be changed with the switch
- Engine runs on gasoline only
- Fuel indicator light on the switch dark or flashing
Common causes of P25A4
- Most likelyOpen wire or unplugged connector at the fuel mode switch
- PossibleFuel mode switch failed internally
- PossibleFaulty connection in a bi-fuel conversion harness
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Fuel mode switch
What each part of P25A4 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| A4 | The exact fault in that area. |
What to do next
- Note P25A4 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P25A4
What does P25A4 mean?
P25A4 means "Fuel Mode Select Switch Circuit". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P25A4?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P25A4 fail an emissions test?
Yes, it can. P25A4 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P25A4 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P25A4 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.