OBD-II reference

All 9.533 generic OBD-II codes, explained in detail.

Causes, inspection steps and sources — a comprehensive DIY archive. Created and maintained with love for the detail. Good luck and have fun!

Powertrain generic / SAE

P25A4

Fuel Mode Select Switch Circuit

General electrical fault on the fuel mode select switch — used on bi-fuel vehicles (CNG/LPG/H2/gasoline) so the driver can pick the active fuel. With the input invalid, the ECM falls back to the default fuel and disables operator-selectable switching.

SystemPowertrain
Typegeneric / SAE
GroupP2
Range / number5 / A4

Possible causes

  • Open or shorted switch wire high

Inspection / repair

  • Difficulty: medium
  • DIY: possible
  • Estimated cost: 60–350 €
  • Estimated time: 0.3–1.5 h
  • Component: fuel mode switch
  • MIL / check engine light

Sources

References

How to read OBD-II codes

The first letter names the vehicle system, the second digit distinguishes generic from manufacturer-specific, the remaining digits group fault area and number.

PPowertrain: engine, transmission, emissions
BBody: chassis trim, comfort, interior
CChassis: suspension, brakes, steering
UNetwork: CAN, control modules, communication