P0039
Turbocharger/Supercharger Bypass Valve A Control Circuit Range/Performance
Turbo / boost control
Generic OBD-II
High
What it means
P0039 means the engine computer sees the turbo (or supercharger) bypass valve control circuit behaving outside its expected range — the valve isn't responding the way the ECM commands. It won't strand you, but boost can become erratic and the car may fall into a reduced-power mode until the valve, wiring, or connection is repaired.
High
Can I keep driving? Usually drivable, but the car may drop into a reduced-power limp mode and feel sluggish under boost until it's fixed.
Common symptoms
What you'll notice
- Check-engine light on
- Reduced power or sluggish acceleration, sometimes with limp mode
- Erratic or inconsistent boost pressure
- Whining or hissing noise from the intake under boost
- Slightly reduced fuel economy
Common causes
Most likely first
- Failed or sticking turbo bypass (recirculation/diverter) valveLikely
- Damaged wiring or connector at the bypass valveCommon
- Loose or corroded electrical connections in the control circuitCommon
- Boost/vacuum leak affecting how the valve respondsLess often
- Failed engine control module (ECM) — rareLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check for other boost-control codes to narrow it down.
- Inspect the bypass valve connector and wiring for damage, looseness, or corrosion.
- Test the bypass valve for correct operation and resistance; replace it if it sticks or reads out of spec.
- Check the intake and boost plumbing for leaks that could skew valve response.
- If wiring and valve are good, consider the ECM last. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0039?+
For short trips usually yes, but expect reduced power. Boost control faults can trigger limp mode, so get it fixed before hard driving or towing.
Can I just clear P0039?+
You can, but it will come back within a few drive cycles unless the valve, wiring, or connection causing it is actually repaired.
Related codes
Often seen with P0039
Read & clear P0039 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX