P25C3 code meaning
Alternative Fuel Disable Signal Circuit Low
Powertrain system Generic code P25xx codes Check engine light
What P25C3 means
P25C3 is logged when the alternative fuel disable signal reaching the engine controller is too low to be valid. A short to ground on the way from the gas system, a gas controller that has lost its supply, or a damaged output stage in that controller can each pull the line down. On a gas installation that announces a block by grounding the line, this would also be indistinguishable from a genuine stop request, so the engine controller has to treat gas operation as unavailable. GM's 2016 bi-fuel trucks illustrate the fallback: they start on gasoline and only change over once the conditions for gas operation have been met, and a failed changeover is shown with the fuel indicator. No manufacturer documents P25C3 publicly. The general signal fault is P25C1, the opposite case P25C2.
P25C3 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P25C3
- No change-over to gas operation
- Fuel mode indicator flashes or shows a fault
- Check engine lamp
Common causes of P25C3
- Most likelySignal wire shorted to ground
- PossibleGas controller without supply voltage
- Less likelyDamaged output stage in the gas controller
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Alt fuel control moduleWiring harness
What each part of P25C3 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. |
| C3 | The exact fault in that area. |
What to do next
- Note P25C3 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 P25C3
What does P25C3 mean?
P25C3 means "Alternative Fuel Disable Signal Circuit Low". P25C3 is logged when the alternative fuel disable signal reaching the engine controller is too low to be valid. It is a generic code, so it means the same on every make.
Is it safe to drive with P25C3?
Drive gently and only to a workshop. With P25C3 the car can go into limp mode (reduced power) to protect itself.
Will P25C3 fail an emissions test?
Yes, it can. P25C3 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 P25C3 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P25C3 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.