P1690 — Volkswagen — MIL Malfunction

P1690 (Volkswagen): MIL Malfunction — what it means, the affected system and what to check before replacing parts.

Meaning, symptoms, causes and checks

MIL Malfunction. Source catalogue definition; confirm applicability using vehicle service information.

Affected system: Powertrain

Symptoms

  • Engine fails to start
  • MIL (Malfunction Indicator Lamp) illuminated
  • Immobilizer warning light flashing
  • Engine starts then immediately stalls

Possible causes

  • Faulty immobilizer control module
  • Communication failure between ECU and immobilizer
  • Damaged or corroded wiring harness
  • Defective transponder key chip
  • Faulty immobilizer antenna coil

What to check

  • Scan for additional immobilizer-specific error codes
  • Inspect the wiring between the ECU and the immobilizer module for continuity
  • Test the immobilizer antenna coil for correct resistance values
  • Verify the integrity of the transponder key signal
  • Check the battery voltage and grounding points for stability