P25C0

Code

Generic P — Powertrain

Alternative Fuel Disable Control Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 22 EN: 37 RU: 26

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Page language: EN

Causes

Short to ground in the disable control wiring
Failed alternative fuel disable solenoid, valve, or switch (internal short)
Faulty relay or driver device in the fuel disable circuit
Poor or corroded connector or terminal at component or ECM
Blown or loose fuse or poor ground connection
Faulty ECM/powertrain control module output (less common)

Symptoms

MIL/Check Engine lamp illuminated
Loss of alternative fuel operation or stuck in primary fuel mode
Vehicle runs only on gasoline or only on alternative fuel
Inconsistent switching between fuel sources
Possible drivability issues during fuel source transition

What to check

Read and record freeze frame and related stored data
Inspect wiring, connectors, and harness for visible damage at the alternative fuel disable component and ECM
Verify fuses and relays for the alternative fuel system
Measure voltage at the disable control connector with key ON (engine OFF) and while commanding enable/disable
Perform wiggle test on wiring while monitoring the signal
Check for related codes that could indicate underlying faults (power, ground, communication)

Signal parameters

Expected inactive/open voltage: approximately battery voltage (≈11–14 V) at the control circuit
Expected active/disabled voltage: low (≈0–1 V) when the ECM or switch pulls circuit low)
Resistance of typical solenoid/valve coil: varies by design (measure coil resistance per service data) — not open or short-circuit
Continuity to chassis ground should be high when circuit is inactive (no unintended short)
If PWM is used, duty cycle will change when commanded — use scope to verify waveform

Diagnostic algorithm

Retrieve DTCs and freeze-frame data. Note operating conditions when fault set.
Visually inspect connectors, pins, and wiring at the alternative fuel disable device, associated relay, fuse box, and ECM. Repair obvious damage.
With key ON (engine OFF), back-probe the disable control harness connector and measure voltage. Compare to expected inactive voltage (battery voltage).
Command the disable function via scan tool (if available) or operate the vehicle function and observe the circuit voltage change. Confirm proper transition between high and low states.
If circuit is low when it should be high, disconnect the disable device connector and measure voltage at the harness pin to isolate: a) if harness still low — suspect short to ground or ECM driver; b) if harness returns to high — suspect component or wiring to ground.
Check coil/valve resistance of the disable device against service spec. Replace if open or shorted.
Inspect and test related relay and fuses. Replace if faulty.
Use a lab scope to inspect waveform if the circuit is PWM‑controlled to confirm driver performance and intermittent faults.
Repair identified wiring faults (repair/replace harness, pins, connectors). Clear codes and verify repair by road test and re-check for DTC return.
If all wiring and component checks are good and the circuit still behaves low, consider ECM/PCM diagnosis or replacement only after thorough verification.

Likely causes

Connector pin pushed out/corroded at disable solenoid
Disable solenoid coil shorted to ground
Relay stuck closed or relay control circuit shorted
Wire insulation damaged and contacting chassis ground
ECM output transistor failed low

Fault status

⚠️ Status

P25C0 — Alternative Fuel Disable Control Circuit Low: The control circuit for the alternative fuel disable/kill function is reporting an unexpectedly low voltage (circuit pulled to ground). Inspect wiring, connectors, and the disable device; verify fuses and relays; test ECM output if wiring and component check good.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours