The turbocharger bypass valve A is the compressor recirculation (diverter) valve: it connects the pressure side of the compressor with the intake side upstream of the turbocharger. It opens when the throttle closes quickly at high boost, so the compressor does not surge and the compressor wheel keeps its speed for the next acceleration. It is not the wastegate, which bypasses exhaust gas around the turbine and has its own codes. The valve is either electric or a vacuum unit controlled by a solenoid. With P0039 the circuit is electrically intact, but the valve does not behave as commanded. On valves with a position sensor, for example, the valve must reach its rest position within a set time after being switched off; the code is set if the measured position deviates too far.
Medium severity. Can I keep driving?Drive without demanding power and go to a repair shop soon. If you see a lot of blue smoke or hear a metallic noise, shut off the engine.
Symptoms
- Check engine light on
- Fluctuating or too little boost
- Loss of power
- Fluttering noise when lifting off the throttle
Most likely causes
- Valve sticking from carbon or oil mist, or diaphragm torn
- Vacuum line or switching valve leaking (pneumatic design)
- Position sensor in the valve faulty
- Increased resistance in the wiring
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P0039 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 0: Subsystem depends on the code range
- 39: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0039?
Drive without demanding power and go to a repair shop soon. If you see a lot of blue smoke or hear a metallic noise, shut off the engine.
What causes code P0039?
The most common causes are: valve sticking from carbon or oil mist, or diaphragm torn; vacuum line or switching valve leaking (pneumatic design); position sensor in the valve faulty.
Related codes
- P0033Turbocharger/Supercharger Bypass Valve A Control Circuit
- P0034Turbocharger/Supercharger Bypass Valve A Control Circuit Low
- P0035Turbocharger/Supercharger Bypass Valve A Control Circuit High
- P2261Turbocharger/Supercharger Bypass Valve A - Mechanical
- P00C3Turbocharger/Supercharger Bypass Valve B Control Circuit Range/Performance
- P0299Turbocharger/Supercharger A Underboost Condition
Sources
- law.cornell.edu: 13 CCR 1968.2
- gsi.ext.gm.com: 19OBDG03A Diagnostics
- ms-motorservice.com: electric recirculating air valves
- en.wikipedia.org: Blowoff valve
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.