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Engine and gearbox (P)

P0039: Turbo/Supercharger Bypass Valve A Issue

This code indicates a problem with the control circuit of the turbocharger or supercharger bypass valve A. The valve is not responding as expected, causing boost pressure to deviate from the target.

Checked by a licensed car technician · last reviewed 30 September 2026

Symptoms

  • Reduced engine power
  • Check engine light on
  • Poor acceleration
  • Unusual engine noises

Common causes

  1. Wastegate sticking from carbon
  2. Vacuum or boost line leaking
  3. Wastegate actuator worn

How to check it yourself

  1. Inspect vacuum and boost lines for leaks
  2. Check wastegate for carbon build-up
  3. Test wastegate actuator function

Can I keep driving?

The car can be driven, but performance may be reduced.

General guidance, not a professional inspection. Confirm faults with measurements before buying parts, and use a qualified mechanic for brakes, steering, fuel leaks, airbags, and other safety-critical work. Terms and disclaimer

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