P25BE

Code

Generic P — Powertrain

Alternative Fuel Disable Control Circuit/Open

Brand: Generic

Type: P — Powertrain

Views: UK: 21 EN: 24 RU: 22

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Page language: EN

Causes

Open or damaged wiring between ECM and alternative-fuel disable device (solenoid/relay/valve)
Disconnected, corroded or bent connector pins at the device or module
Blown fuse or faulty relay supplying the disable circuit
Failed disable device (solenoid, valve or actuator) with open coil
Poor or missing ground at the disable device or ECM
Aftermarket or retrofit alternative fuel equipment with improper wiring

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Vehicle may not switch to alternative fuel or alternative-fuel mode is disabled
Possible reduced fuel economy if stuck on less efficient fuel
No obvious drivability issue if the system simply remains disabled
Stored trouble code and possible reduced power depending on system design

What to check

Read freeze frame and stored data with a scan tool; note operating conditions when code set
Visual inspection of wiring and connectors for damage, corrosion, disconnection, or aftermarket splices
Check fuses and relays related to the alternative fuel system
Backprobe the disable device connector while commanding the device on/off with a scanner
Measure supply voltage and ground continuity at the device connector
Check coil resistance of the disable solenoid/valve (compare to service info if available)

Signal parameters

Control line typically is a switched 12 V supply or a switched ground from the ECM; expected battery voltage (~12 V) when commanded on
When circuit is open: infinite resistance (OL) or no continuity between ECM and device
When device energized: coil resistance should be finite (manufacturer-specific — compare to spec) and current draw should rise from idle
Command may be steady or PWM; scope should show commanded waveform when ECM outputs are active
Ground continuity: low resistance to chassis ground (< a few ohms) expected at device ground

Diagnostic algorithm

Retrieve code(s) and freeze-frame data; note conditions (engine temp, RPM, battery voltage).
Perform a visual inspection of the alternative-fuel system wiring, connectors, and control module for damage or corrosion.
Check related fuses and relays; replace if blown or faulty and clear the code to see if it returns.
Identify the disable device (solenoid/valve/relay). With ignition off, disconnect connector and check for open circuit or poor terminals.
Measure coil resistance of the disable device; if infinite/open, replace the device.
With connector connected, backprobe and command the disable device ON with a scan tool. Verify expected voltage or ground signal at the connector and that the device actuates.
If no command from ECM, test continuity between the ECM and the device; repair any open wiring or poor terminals.
Check and repair grounds related to the circuit; ensure good chassis/ECM grounds.
After repairs, clear codes and perform functional test and road test; verify code does not return and alternative-fuel operation is restored.
If wiring and device check good but no ECM command, consider ECM/controller diagnosis or replacement per manufacturer procedures.

Likely causes

Broken wire or connector between ECM and alternative-fuel disable solenoid
Open coil in the disable solenoid or valve
Blown fuse or bad relay in the disable circuit power feed
Corroded terminal or poor ground at the device
Faulty aftermarket control module or incorrect installation

Fault status

⚠️ Status

Alternative Fuel Disable Control Circuit/Open — open or interrupted electrical circuit preventing proper control of the alternative-fuel disable device. Inspect wiring, connectors, fuses/relays, grounds, and the disable device.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours