Fuel and air

P0039 — Turbo/Supercharger Bypass Valve Control Circuit Range/Performance

Severity: medium Drive with care, to a shop

What P0039 means

P0039 sets when the engine control module sees a mismatch between its command to the turbo or supercharger bypass valve and the valve's actual response or circuit signal. This valve releases excess boost pressure when the throttle closes, protecting the turbo and intake plumbing from pressure spikes. When a fault is found, the module may limit boost and power.

Symptoms

  • Check Engine light on
  • Loss of power and sluggish acceleration
  • Low or unstable boost pressure
  • Hissing or unusual noises from the turbo or hoses
  • Limp mode
  • Flutter or surging when lifting off the throttle

Possible causes

  1. Faulty bypass valve or its solenoid
  2. Damaged wiring or corroded, loose connector in the control circuit
  3. Open circuit or short to ground or power in the harness
  4. Faulty boost pressure sensor giving wrong readings
  5. Vacuum leaks or collapsed vacuum hoses (if the valve is vacuum operated)
  6. Sticking valve or torn diaphragm
  7. Rarely, a PCM or boost controller fault

How to diagnose

  1. Scan for all codes and review freeze frame data, noting any other boost-related codes
  2. Inspect the valve, boost pipes and vacuum hoses for cracks, leaks and oil residue
  3. Check the valve connector and harness for corrosion, chafing or breaks
  4. Measure the valve coil resistance and compare it to the manufacturer's spec
  5. Check for power and control signal at the connector with a multimeter or scope
  6. Command the valve with a scan tool and see whether it responds
  7. Check the boost pressure sensor readings and pressure-test the intake tract for leaks
  8. Test the vacuum actuator with a hand vacuum pump, if fitted

Common fixes

  • Replace the bypass valve
  • Repair the wiring or replace the damaged connector
  • Replace the boost pressure sensor
  • Replace cracked or collapsed vacuum hoses and fix leaks
  • Update software or replace the PCM once it is confirmed faulty

Questions and answers

What does P0039 mean?

The engine computer found that the turbo or supercharger bypass valve control isn't behaving as expected. The cause can be an electrical circuit problem or a mechanical problem with the valve itself.

Can I drive with a P0039 code?

Short, gentle trips are usually possible, but power may be limited. Don't put off repairs, as the turbocharger could be damaged.

What should I check first for P0039?

Start by inspecting the wiring, the valve connector and the vacuum hoses. Then test the valve with a scan tool and check the boost pressure sensor readings.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.