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!

Chassis generic / SAE

C0399

4WD Mode Switch Circuit Malfunction

The transfer case or 4WD control module has detected an invalid signal from the driver-operated 4WD mode selector. Mode requests from the dashboard may be ignored.

SystemChassis
Typegeneric / SAE
GroupC0
Range / number3 / 99

Possible causes

  • Mode selector switch failed high
  • Wiring or connector fault medium

Symptoms

  • ABS warning light on
  • ESC/stability control deactivated
  • Possible reduced brake assist
  • Speedometer may behave erratically

Inspection / repair

  • Difficulty: easy
  • DIY: possible
  • Estimated cost: 60–300 €
  • Estimated time: 0.3–1.5 h
  • Component: mode selector switch
  • Component: transfer case module
  • Component: switch wiring

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