Powertrain, generic (extended)

P25C2 Alternative Fuel Disable Signal Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P25C2 means the alternative fuel disable signal arriving at the engine controller sits above its valid range. Likely explanations are a short to a voltage feed, a missing ground at the gas controller that lets its output float up, or an open line combined with an internal pull-up in the reading module. Whether a high level reads as blocked or as released depends on the design, so the engine controller can no longer trust the gas system's status and will usually stay with or return to gasoline. GM's Impala bi-fuel information shows the logic behind this: with a delivery concern on one side, the ECM moves to the fuel system that is working. No manufacturer documents P25C2 publicly. In the SAE list the High code precedes the Low code here, unlike most groups.

Likely causes

Signal wire shorted to a voltage feed
Missing ground at the gas controller letting its output float high
Open signal wire pulled up inside the reading module

Symptoms

  • Vehicle stays on gasoline
  • Gas system fault indication
  • Check engine lamp

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–600
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

alt fuel control modulewiring harness

Related codes

P25C1P25C3P25BF

References: static.nhtsa.gov, law.cornell.edu.