P25A6

Code

Generic P — Powertrain

Fuel Mode Select Switch Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 19 EN: 31 RU: 27

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Short to ground in the fuel mode select switch wiring
Open or intermittent wiring/connectors between switch and PCM
Faulty fuel mode select switch (internal short or stuck contact)
Blown fuse or poor power/ground related to the switch circuit
PCM input driver fault or internal PCM damage

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Inability to change fuel mode or vehicle always using a default fuel mode
Fuel mode indicator on dash incorrect or does not respond
Reduced drivability or incorrect fueling when the wrong mode is selected
Stored freeze‑frame and live data shows switch at low/ground state

What to check

Scan the vehicle for stored codes and freeze frame data; record live data for the fuel mode switch
Visually inspect switch, connector, and wiring for damage, corrosion, or poor pin fit
Check related fuses and power/ground circuits for the switch
Backprobe the switch connector and measure voltage with key ON (engine OFF) while operating the switch
Perform a wiggle test on harness while monitoring live data to reproduce the fault
Inspect PCM connector for corrosion or bent pins if wiring/connector at switch looks good

Signal parameters

Typical circuit uses a pull‑up to 5 V (or vehicle reference); valid HIGH ≈ 2.5–5.0 V, valid LOW ≈ 0–0.8 V
Fault condition: signal stuck low (
At switch terminal with key ON and switch in other position expect change in voltage corresponding to switch states (refer to vehicle-specific data)

Diagnostic algorithm

Retrieve freeze frame and detailed live data; note when the fault occurred and switch states
Visually inspect the fuel mode switch, mounting, connector, and wiring for damage, corrosion, or water intrusion
Check fuses and related power/ground circuits; repair any failures
Backprobe switch harness at the connector. With key ON (engine OFF) measure terminal voltage and compare to expected values (see signal parameters). Operate the switch and observe voltage changes.
If voltage is low and does not change, disconnect the switch and check for short to ground between the switch signal wire and chassis using an ohmmeter; repair short if present.
If no short to ground and harness wiring is good, apply a known good 5 V reference/pull‑up (or use jumper per service manual) to the PCM input and verify PCM responds — if PCM input never changes, suspect PCM fault.
If switch is defective or intermittent, replace the fuel mode select switch and retest.
Clear codes and perform a test drive to confirm the repair; verify no recurrence of P25A6 and correct fuel mode operation.

Likely causes

Damaged harness insulation chafed to chassis ground at or near the switch
Corroded/loose connector at the switch or PCM pin
Failed fuel mode select switch contacts causing low output
Blown/weak fuse supplying the switch reference or pull‑up resistor
PCM input damaged by previous short or voltage spike

Fault status

⚠️ Status

PCM detected low voltage on fuel mode select switch circuit. MIL illuminated and freeze frame stored. Manufacturer‑specific troubleshooting required for exact voltage/reference.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours