P25C1 code meaning
Alternative Fuel Disable Signal Circuit
Powertrain system Generic code P25xx codes Check engine light
What P25C1 means
P25C1 relates to the incoming side of the alternative fuel disable function: a signal line on which the engine controller reads whether gas operation is blocked, either as feedback from the gas system or as a request from it, for example when a CNG or LPG controller detects low tank pressure or its own fault. The code says the signal is missing or unusable without naming a direction. In GM's bi-fuel Silverado and Sierra the system changes back to gasoline by itself when the gas tank runs empty and stops toggling after 20 transitions in one key cycle, which shows how much the engine controller depends on knowing the gas system's state. No manufacturer documents P25C1 publicly. P25C2 and P25C3 are the high and low variants; P25BE to P25C0 cover the control output.
P25C1 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 P25C1
- Gas mode unavailable or drops out while driving
- Fuel mode indicator flashes
- Check engine lamp
Common causes of P25C1
- Most likelyOpen signal wire from the gas system
- PossibleGas controller without power or ground, so no signal is sent
- PossibleCorroded underbody connector of the gas system
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Alt fuel control moduleFeedback sensorWiring harness
What each part of P25C1 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. |
| C1 | The exact fault in that area. |
What to do next
- Note P25C1 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 P25C1
What does P25C1 mean?
P25C1 means "Alternative Fuel Disable Signal Circuit". P25C1 relates to the incoming side of the alternative fuel disable function: a signal line on which the engine controller reads whether gas operation is blocked, either as feedback from the gas system or as a request from it, for example when a CNG or LPG controller detects low tank pressure or its own fault. It is a generic code, so it means the same on every make.
Is it safe to drive with P25C1?
Drive gently and only to a workshop. With P25C1 the car can go into limp mode (reduced power) to protect itself.
Will P25C1 fail an emissions test?
Yes, it can. P25C1 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 P25C1 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P25C1 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.