P25C1Alternative Fuel Disable Signal Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Gas mode unavailable or drops out while driving
- Fuel mode indicator flashes
- Check engine lamp
- Likely causes
- 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
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.