P0039 is a diagnostic trouble code that points to a problem with the turbocharger or supercharger bypass control circuit, specifically that it’s reading “range/performance” outside what the ECU expects. In plain terms, your engine computer isn’t happy with how the boost control system is behaving. You might notice low power, odd turbo noises, or even overboost protection kicking in. While it’s not usually an immediate engine-killer, you shouldn’t ignore it. Left unchecked, P0039 can lead to poor drivability, higher fuel use, and potential turbo or engine damage.
What Does P0039 Mean?
P0039 stands for “Turbocharger/Supercharger Bypass Valve Control Circuit Range/Performance.” Your ECU monitors an electronic or vacuum-operated bypass (or wastegate-style) valve that controls how much boost pressure your engine sees. When the signal or behavior from that circuit is outside the expected range, the ECU sets P0039.
This can be due to an electrical issue (wiring, connector, sensor) or a mechanical problem (sticking bypass valve, vacuum leak, incorrect boost response). The code doesn’t tell you which part failed, only that the bypass control system isn’t responding correctly under certain conditions.
Quick Reference
- Code: P0039
- Definition: Turbocharger/Supercharger Bypass Valve Control Circuit Range/Performance
- Typical systems affected: Turbo or supercharger boost control, bypass/wastegate valve
- Common symptoms: Low power, overboost, check engine light, limp mode
- Risk level: Moderate – avoid hard driving until fixed
Real-World Example / Field Notes
On the service side, I see P0039 most often on turbocharged four-cylinder engines that are a few years old and have some miles on them. A typical case: a customer complains of intermittent loss of power and a whooshing sound when accelerating. Scan shows P0039 stored, sometimes along with an overboost or underboost code. After inspection, I often find a cracked vacuum hose to the bypass valve or a sticky valve itself. Fixing the leak or replacing the valve usually restores full boost and clears the code.
Symptoms of P0039
- Check engine light on – P0039 usually sets a steady MIL, sometimes with other boost-related codes.
- Loss of power – You may feel sluggish acceleration, especially when trying to pass or climb hills.
- Erratic boost – Surging, uneven power delivery, or boost that comes on late or too aggressively.
- Limp mode – The ECU may limit boost and throttle response to protect the engine and turbo.
- Unusual turbo noise – Hissing, whooshing, or fluttering sounds under load can indicate bypass issues.
- Poor fuel economy – Incorrect boost control can make the engine run less efficiently.
- Possible detonation or pinging – In some cases of overboost, you may hear spark knock under heavy load.
Common Causes of P0039
Most Common Causes
- Sticking or faulty bypass valve – Carbon buildup, internal wear, or a failed actuator can keep the valve from opening or closing correctly.
- Vacuum hose leaks – On vacuum-operated systems, cracked, loose, or disconnected hoses to the bypass or wastegate actuator are extremely common.
- Electrical connector issues – Corroded, loose, or damaged connectors at the bypass valve solenoid or actuator can cause range/performance faults.
- Failed bypass control solenoid – The solenoid that regulates vacuum or pressure to the valve can fail electrically or stick mechanically.
- Boost leaks – Leaks in intercooler piping, couplers, or the intake tract can cause unexpected boost behavior the ECU flags as P0039.
Less Common Causes
- Damaged wiring harness – Chafed, pinched, or shorted wires between the ECU and bypass control circuit.
- Faulty boost pressure sensor – If the sensor reports incorrect boost, the ECU may think the bypass system is not doing its job.
- ECU software or internal fault – Rare, but outdated calibration or internal ECU failures can misinterpret normal operation as a fault.
- Aftermarket tuning or modifications – Aggressive tunes, manual boost controllers, or non-OEM turbos can push the system outside the factory’s expected range.
- Mechanical turbocharger issues – Sticking wastegate, damaged compressor wheel, or excessive shaft play affecting boost response.
Diagnosis: Step-by-Step Guide
You’ll want a basic tool kit, a quality OBD2 scan tool (ideally one that can read live data and Mode $06), a hand vacuum pump (for vacuum-operated systems), and a digital multimeter. Access to a factory service manual or wiring diagram is very helpful for pinouts and specifications.
- Confirm the code and check for companions
Scan for codes and note any others, especially P0234 (overboost), P0299 (underboost), or sensor-related codes. Multiple codes can point you toward either a control issue or a sensor problem. - Inspect hoses and lines visually
With the engine off, inspect all vacuum and boost hoses around the turbo, intercooler, and bypass valve. Look for cracks, oil saturation, loose clamps, or disconnected lines. Fix anything obvious before going deeper. - Check the bypass valve and actuator
Locate the turbo/supercharger bypass or wastegate-style valve. Manually move the linkage if accessible. It should move smoothly without binding. Any stiffness, sticking, or obvious damage means the valve likely needs replacement. - Test vacuum-operated systems
If your system uses vacuum, connect a hand vacuum pump to the actuator. Apply vacuum and watch for movement and whether it holds vacuum. If it doesn’t move or leaks down quickly, the actuator diaphragm is likely bad. - Test the control solenoid
Unplug the bypass control solenoid. Using a multimeter, check resistance across the solenoid terminals and compare to spec from the service manual. An open circuit, short, or wildly out-of-range reading indicates a failed solenoid. - Check power, ground, and signal
With the key on, use a wiring diagram to verify that the solenoid or electronic actuator is getting proper power and ground. Then check the control or feedback signal wire for correct voltage or duty cycle as commanded by the ECU. - Review live data and boost behavior
On a road test (or controlled dyno run), monitor boost pressure, bypass valve command, and related PIDs. Look for mismatches between commanded and actual boost. This can help you pinpoint whether the issue is mechanical or electrical. - Check Mode $06 and freeze frame
Use Mode $06 data (if your scan tool supports it) to see which test failed and under what conditions. Freeze frame data from when P0039 set can tell you engine load, RPM, and boost at the time of failure. - Inspect wiring harness
If all components test good, carefully inspect the harness from the ECU to the bypass valve/solenoid. Look for rubbing on brackets, heat damage near the turbo, or previous repairs that may be failing. - Clear the code and retest
After repairs, clear codes and perform a proper drive cycle, including moderate boost conditions. Confirm that P0039 does not return and that boost response feels normal.
Pro tip: Don’t skip the simple visual and vacuum tests. I’ve seen many P0039 diagnoses overcomplicated when the real issue was a $5 cracked hose or a loose clamp on an intercooler pipe.
Possible Fixes & Repair Costs
Fixing P0039 usually focuses on restoring proper control of the turbo/supercharger bypass system. Common repairs include replacing cracked vacuum hoses, installing a new bypass valve or actuator, replacing a failed control solenoid, repairing wiring, or addressing boost leaks in the intercooler plumbing. In some cases, a software update or ECU reflash may be recommended by the dealer.
Typical repair costs vary widely depending on the root cause and the vehicle. Simple vacuum hose or clamp repairs can run $50–$150. A new bypass valve or actuator usually falls in the $200–$500 range parts and labor. Replacing a control solenoid often costs $150–$350. If there are major turbocharger issues or extensive wiring repairs, you could see $600–$1,200 or more. Labor rates, parts availability, and how buried the turbo system is in your engine bay all affect the final bill.
Can I Still Drive With P0039?
In many cases, you can still drive with P0039 without immediate catastrophic damage, especially if the car is just slightly down on power and not showing severe symptoms. However, it’s not wise to ignore it or continue aggressive driving. If the ECU is detecting improper boost control, you could be running with either too little or too much boost. Underboost will hurt performance and fuel economy; overboost can damage pistons, head gaskets, or the turbo itself. Until you diagnose and repair the issue, drive gently and avoid heavy throttle or long highway pulls.
What Happens If You Ignore P0039?
Ignoring P0039 can turn a relatively small problem into a big one. Continued driving with improper boost control can lead to turbo failure, detonation, excessive exhaust temperatures, and even internal engine damage. You may also see more frequent limp mode events and worsening fuel economy. Addressing the code early usually keeps the repair simpler and cheaper.
Related Codes
- P0027 – Exhaust Valve Control Solenoid Circuit Range/Performance Bank 1
- P0026 – Intake Valve Control Solenoid Circuit Range/Performance Bank 1
- P0019 – Crankshaft Position Camshaft Position Correlation Bank 2 Sensor B
- P0018 – Crankshaft Position Camshaft Position Correlation Bank 2 Sensor A
- P0017 – Crankshaft Position Camshaft Position Correlation Bank 1 Sensor B
- P0016 – Crankshaft Position Camshaft Position Correlation Bank 1 Sensor A
- P0009 – Engine Position System Performance Bank 2
- P0008 – Engine Position System Performance Bank 1
- P0007 – Fuel Shutoff Valve “A” Control Circuit High
- P0006 – Fuel Shutoff Valve “A” Control Circuit Low
Key Takeaways
- P0039 means the ECU sees abnormal behavior in the turbo/supercharger bypass valve control circuit.
- Common causes include bad bypass valves, vacuum leaks, faulty solenoids, and wiring issues.
- Symptoms often include a check engine light, low power, erratic boost, and sometimes limp mode.
- Diagnosis should combine visual inspection, vacuum testing, electrical checks, and live data review.
- Repairs can be relatively inexpensive if caught early, but ignoring the code risks turbo and engine damage.
Vehicles Commonly Affected by P0039
P0039 shows up most often on modern turbocharged gasoline engines. You’ll see it on many Subaru WRX/Forester/Outback turbo models, various Volkswagen and Audi 1.8T and 2.0T engines, Ford EcoBoost vehicles (Focus, Fusion, F-150), GM turbocharged models (Cruze, Regal, Sonic), and some Hyundai and Kia turbo applications. It can also appear on supercharged engines from manufacturers like Mercedes-Benz and Jaguar. Any vehicle that uses an electronically or vacuum-controlled bypass or wastegate valve can potentially set this code when the system isn’t responding as designed.
FAQ
Can P0039 cause engine damage?
Yes, if the underlying issue leads to sustained overboost or severe detonation, P0039 can be associated with engine damage over time. The code itself is just a warning, but the conditions causing it—especially a stuck-closed bypass or wastegate problem—can stress pistons, head gaskets, and the turbocharger. Fixing the cause promptly greatly reduces the risk.
Is P0039 always a turbo failure?
No. A failed turbo is actually one of the less common causes. More often, P0039 is triggered by a bad bypass valve, a faulty solenoid, vacuum leaks, or wiring issues. A proper diagnosis can save you from replacing an expensive turbo that isn’t actually the problem.
Can I clear P0039 and keep driving?
You can clear the code with a scan tool, but if the underlying fault is still present, P0039 will usually return once the same conditions are met. Clearing it without fixing the cause just hides the symptom temporarily and may allow a small issue to become a larger, more expensive one.
How serious is P0039 compared to other codes?
P0039 is moderately serious. It’s not like a low-oil-pressure or overheating situation where you must stop immediately, but it’s more than a minor emissions code. Because it affects boost control, it impacts performance, fuel economy, and long-term reliability. Plan to diagnose and repair it soon rather than later.
Can a tune or aftermarket boost controller cause P0039?
Yes. Aftermarket tunes, manual boost controllers, or non-stock turbos can push the system outside the factory’s expected boost and bypass behavior. The ECU may see this as a range/performance problem and set P0039. If you’ve modified your car, you may need a proper custom tune and to verify that the bypass and wastegate systems are still operating within safe limits.