P0039: Turbocharger/Supercharger Bypass Valve Control Circuit Range/Performance

What it means

The turbocharger or supercharger bypass valve control circuit is not performing within the expected range.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

The turbocharger or supercharger bypass valve routes air around the compressor to help control boost and engine response. The module sets P0039 when the bypass valve control circuit or its response falls outside the expected range, which may result from a sticking mechanism, leaking boost or vacuum line, or worn actuator.

Common causes

Most likely first.

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

Symptoms

• Check engine light on
• Reduced engine performance

How to diagnose it

1. Record freeze-frame data and review boost, bypass-valve command, and related position readings with a scan tool to identify when performance falls outside the expected range.
2. Inspect the bypass valve, actuator, and connecting hoses for loose fittings, splits, leaks, or signs of sticking.
3. Check the actuator linkage for wear or binding and confirm that it moves as commanded using the manufacturer's test procedure.
4. Test the bypass valve control wiring and connectors for damage or poor connections, then check actuator operation against the manufacturer's specification.
5. If the control circuit works correctly, assess the valve and boost system for mechanical sticking or leaks under the manufacturer's procedure.

Common fixes

• Reconnect or replace a leaking vacuum or boost line.
• Repair damaged bypass-valve control wiring or connector contacts.
• Clean or repair a sticking bypass valve if permitted by the manufacturer's procedure.
• Replace a worn actuator or bypass-valve component that fails testing.

Can I keep driving?

Reduced power or limp mode may make merging and passing unsafe, so avoid hard acceleration and boost-heavy driving. If power drops sharply, the engine runs abnormally, or the vehicle cannot keep up safely with traffic, stop in a safe place and arrange assistance.