P0033 is a trouble code you usually see on turbocharged or supercharged engines, and it points to a problem with the turbocharger bypass valve control circuit. In plain English, the computer isn’t happy with how the blow-off or bypass valve is being controlled. You might hear odd whooshing noises, feel a loss of power, or just see the check engine light with no other symptoms. This code isn’t usually an immediate engine killer, but it can hurt performance and, if ignored, can lead to more expensive turbo-related repairs.
What Does P0033 Mean?
P0033 stands for “Turbocharger Bypass Valve Control Circuit.” Your engine control unit (ECU) uses an electrical signal to control a bypass or blow-off valve that regulates boost pressure. When the ECU detects an electrical issue in that circuit—open, short, or out-of-range signal—it stores P0033.
This code is about the control circuit, not the mechanical side of the turbo itself. The valve, the wiring, or the solenoid that operates the valve may be faulty, or the ECU may be seeing a voltage or duty-cycle signal it doesn’t expect.
Quick Reference
- Code: P0033
- Definition: Turbocharger Bypass Valve Control Circuit
- System: Turbo/supercharger boost control
- Severity: Low to moderate, but can affect performance
- Common Causes: Bad bypass solenoid, wiring issues, stuck valve, vacuum leaks
Real-World Example / Field Notes
In the shop, I see P0033 most often on small turbocharged four-cylinders—think VW/Audi 1.8T/2.0T, Ford EcoBoost, GM 1.4T/2.0T, and some Subaru models. A common pattern is a customer complaining of a loud “psshh” sound, slower acceleration, or an intermittent check engine light after installing an aftermarket blow-off valve or intake. Many times, the problem ends up being a cracked vacuum hose to the bypass valve or a cheap aftermarket solenoid that doesn’t match the factory electrical specs. Fixing the plumbing and going back to an OEM-quality valve usually clears P0033 quickly.
Symptoms of P0033
- Check engine light (MIL) illuminated, sometimes with no obvious drivability issues.
- Loss of power or sluggish acceleration, especially under boost.
- Unusual turbo noises like loud whooshing, flutter, or chirping when you lift off the throttle.
- Poor fuel economy due to improper boost control and richer mixtures.
- Intermittent surging or inconsistent boost pressure while accelerating.
- Hesitation or stumble when transitioning into or out of boost.
- Other boost-related codes stored alongside P0033, such as underboost or overboost.
Common Causes of P0033
Most Common Causes
- Faulty turbo bypass (diverter) valve solenoid: Internal electrical failure, high resistance, or stuck solenoid plunger.
- Damaged wiring or connector: Corroded pins, broken wires, loose connector at the bypass valve or harness.
- Vacuum hose issues: Cracked, split, or disconnected vacuum lines feeding the bypass valve on vacuum-operated systems.
- Aftermarket modifications: Non-OEM blow-off valves, boost controllers, or intake systems that change the control signal or plumbing.
- Stuck or leaking bypass valve: Valve stuck open or closed, or diaphragm torn, affecting how the circuit responds.
Less Common Causes
- ECU driver failure: Rare, but the internal transistor that controls the valve can fail, causing incorrect voltage or duty cycle.
- Short to power or ground elsewhere in harness: Chafed wiring harness contacting metal, causing intermittent circuit faults.
- Poor engine ground connections: High resistance grounds can skew voltage readings in the control circuit.
- Incorrect repairs or splices: Previous wiring repairs using wrong gauge wire, twist-and-tape splices, or poor-quality connectors.
- Software/flash issues: On tuned vehicles, aggressive boost maps or incorrect coding can trigger circuit-related codes.
Diagnosis: Step-by-Step Guide
To diagnose P0033 properly, you’ll want at least a decent scan tool (preferably with live data and Mode $06), a digital multimeter, basic hand tools, and possibly a handheld vacuum pump. Access to a wiring diagram for your specific vehicle is a big help.
- Verify the code and check for companions. Connect a scan tool, confirm P0033 is present, and look for related boost or circuit codes (like P0243, P0299). Note freeze-frame data—engine load, RPM, and boost when the code set.
- Perform a visual inspection. With the engine off, inspect the bypass valve, solenoid, and surrounding area. Look for broken connectors, chafed wiring, oil contamination in plugs, and loose or missing mounting hardware.
- Inspect vacuum lines (if equipped). On vacuum-operated systems, check all hoses to and from the bypass valve. Replace any that are brittle, cracked, swollen, or oil-soaked. Confirm hoses are routed correctly per the under-hood diagram.
- Check electrical connectors. Unplug the bypass solenoid and inspect the terminals. Clean any green corrosion, bent pins, or moisture. Apply dielectric grease and ensure the connector locks firmly.
- Test solenoid resistance. Using a multimeter, measure resistance across the solenoid terminals and compare to spec (often in the 20–40 ohm range, but check service data). Infinite resistance indicates an open coil; near zero suggests a shorted coil.
- Verify power and ground. With the key ON, use the multimeter to check for proper voltage supply at the solenoid connector and a good ground or control signal from the ECU. Back-probe if necessary; avoid damaging terminals.
- Command the valve with a scan tool. Many scan tools let you activate the bypass valve via bi-directional controls. Listen and feel for the solenoid clicking. If it doesn’t respond but power/ground are good, the solenoid is likely bad.
- Check mechanical operation. On some systems, you can apply vacuum with a hand pump to the valve and confirm it moves and holds vacuum. If it leaks down quickly or doesn’t move, the valve is mechanically faulty.
- Inspect harness routing. Follow the wiring back toward the ECU, looking for spots where the harness rubs on brackets or the engine. Repair any damaged sections with proper solder/heat-shrink or OEM-style connectors.
- Clear codes and road test. After repairs, clear P0033 and perform a controlled road test with live data. Monitor boost pressure, commanded bypass duty cycle, and see if the code returns under similar conditions.
Pro tip: On tuned or modified cars, always return to stock boost control hardware and maps while diagnosing P0033. Aftermarket parts can mask the real problem or create false circuit faults that waste your time.
Possible Fixes & Repair Costs
Most repairs for P0033 are straightforward once you pinpoint the cause. Common fixes include replacing the turbo bypass valve or solenoid, repairing or replacing damaged wiring/connectors, reinstalling proper vacuum hoses, or undoing poorly installed aftermarket boost control parts. In rare cases, an ECU repair or replacement is needed.
Typical repair costs vary widely. A new bypass solenoid or valve can run $75–$300 for parts, plus $80–$200 in labor depending on access. Wiring repairs may cost $100–$250 if harness work is involved. An ECU replacement or reflash can range from $400–$1,200. Factors affecting cost include vehicle make, turbo layout, labor rates in your area, and whether OEM or aftermarket parts are used.
Can I Still Drive With P0033?
In most cases, you can still drive with P0033 without immediate engine damage, especially if the car only shows a check engine light and mild performance changes. However, you may notice reduced power, inconsistent boost, or higher fuel consumption. If you hear loud turbo noises, experience severe loss of power, or the car goes into limp mode, you should avoid hard acceleration and have it inspected as soon as possible. Long-term driving with improper boost control is not recommended.
What Happens If You Ignore P0033?
If you ignore P0033, you risk running the engine with unstable or incorrect boost levels. Over time, that can stress the turbocharger, intercooler hoses, and engine internals. You may also foul spark plugs, clog the catalytic converter from rich mixtures, and end up with more serious and expensive issues than a simple valve or wiring repair.
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
- P0033 points to an electrical problem in the turbocharger bypass valve control circuit, not necessarily a bad turbo.
- Common causes include a failed bypass solenoid, damaged wiring, vacuum leaks, or aftermarket modifications.
- Symptoms range from a simple check engine light to loss of power, odd turbo noises, and poor fuel economy.
- Diagnosis involves checking wiring, vacuum lines, solenoid resistance, and using a scan tool for live data and active tests.
- Repairs are often affordable if handled early; ignoring the code can lead to more serious turbo and engine issues.
Vehicles Commonly Affected by P0033
P0033 is most common on modern turbocharged vehicles. You’ll see it frequently on Volkswagen and Audi 1.8T and 2.0T engines, Ford EcoBoost models (Focus, Fusion, F-150), GM turbo engines (Chevy Cruze, Sonic, Malibu, Buick Regal), and various Subaru WRX/Forester XT models. It can also show up on turbocharged Volvos, BMWs, and some Kia/Hyundai GDI turbo engines. Any vehicle with a computer-controlled bypass or diverter valve can set P0033 when the control circuit isn’t behaving as expected.
FAQ
Can P0033 damage my engine?
By itself, P0033 usually doesn’t cause immediate engine damage, but it indicates that boost control isn’t working correctly. If the bypass valve fails in a way that causes chronic overboost or unstable boost, long-term stress on the turbo and engine components can lead to more serious failures.
Is P0033 caused by a bad turbocharger?
Not usually. P0033 is about the bypass valve control circuit, not the turbocharger itself. A worn turbo can contribute to boost issues, but the code typically points to the solenoid, valve, wiring, or vacuum lines that control boost, rather than the turbo’s bearings or compressor wheel.
Can I clear P0033 and keep driving?
You can clear the code with a scan tool, and it may stay off for a while if the problem is intermittent. However, if the underlying issue isn’t fixed, P0033 will usually return under similar driving conditions. It’s better to diagnose and repair the cause than to repeatedly clear the code.
How serious is P0033 compared to other turbo codes?
P0033 is generally less critical than severe overboost or underboost codes like P0234 or P0299, but it still matters. It often appears early in the failure chain, giving you a chance to fix a small electrical or vacuum issue before it causes major drivability problems.
Can aftermarket blow-off valves cause P0033?
Yes, aftermarket blow-off or diverter valves are a common trigger for P0033, especially if they’re not designed to work with your car’s ECU strategy. Incorrect spring rates, plumbing changes, or different electrical characteristics can confuse the ECU and set a circuit fault. Sticking with OEM or high-quality, vehicle-specific parts helps avoid this.