Powertrain, generic (extended)

P25BE Alternative Fuel Disable Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P25BE concerns the output with which the engine controller tells an alternative fuel system, usually a CNG or LPG installation, to stop gas operation, for example after a fault, with an empty gas tank or while the engine warms up. The code reports an open circuit or a driver fault on this control line, so the command may no longer reach the gas controller or its shut-off valves. GM describes bi-fuel vehicles such as the Impala with the LFR engine, where one ECM runs both fuel systems and switches to the healthy one if a delivery problem appears; LPG retrofits often add a separate gas controller. No manufacturer documents P25BE publicly. CARB treats such a vehicle as alternate-fueled only while it burns the gas fuel. The vehicle normally keeps running on gasoline.

Likely causes

Open control wire between engine controller and gas system
Poor splice or connector in a retrofit gas installation
Open coil in a gas disable relay
Output driver in the engine controller defective

Symptoms

  • Vehicle stays on gasoline or will not switch to gas
  • Fuel mode indicator flashes or shows a system fault
  • 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 modulealt fuel disable relaywiring harness

Related codes

P25BFP25C0P25C1P25A4

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