Powertrain, generic (extended)

P25C0 Alternative Fuel Disable Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P25C0 is set when the alternative fuel disable output reads too low, typically a short to ground somewhere between the engine controller and the gas system. With a high-side driver that pin would then be unable to deliver its voltage; with a low-side driver the line would look permanently switched. The practical risk lies in which state the gas system reads as safe: if a missing block signal were taken as permission, gas could be released when the controller wants it off, so controllers generally stop gas operation as soon as such a fault is confirmed. CARB requires every 2019 and later alternate-fueled vehicle to run under an approved monitoring plan, which is where checks like this belong. No manufacturer documents P25C0 publicly; the open circuit is P25BE, the high fault P25BF.

Likely causes

Control wire shorted to ground, often where routed along the frame
Chafed insulation on a retrofit gas kit harness
Output stage in the engine controller damaged

Symptoms

  • Vehicle refuses to switch to gas
  • Fuel system fault message or flashing fuel indicator
  • 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

P25BEP25BFP25C3

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