P0033
PowertrainTurbo Charger Bypass Valve Control Circuit
The turbocharger bypass valve (the part that bleeds off boost pressure so the turbo doesn't overspeed or build too much pressure) is controlled by a solenoid or actuator, and the ECU has spotted an electrical fault in that control circuit. When it can't control boost properly, you'll usually get reduced power and the engine dropping into limp mode to protect itself. On a lot of cars this is wiring or a tired solenoid rather than the turbo itself, which is the bit that saves your wallet.
ⓘ Information only. This page provides general educational information about fault code P0033. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0033 mean?
P0033 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Turbo Charger Bypass Valve Control Circuit.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, sometimes with a flashing power-restricted message on the dash
- • Obvious loss of pull, especially when you put your foot down to overtake on the motorway
- • Limp mode kicking in, leaving you with sluggish throttle and a hard rev limit
- • Whistling or fluttering noise from the turbo area as boost isn't being managed properly
- • Black smoke from the exhaust on diesels under load
- • Hesitation or a jerky surge during hard acceleration
Possible causes
Causes commonly associated with P0033, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Faulty bypass valve solenoid or electronic actuator, the usual culprit on higher-mileage cars where the unit has worn or stuck
- 2. Wiring or connector fault in the control circuit, often corrosion or a chafed wire near the hot turbo, which throws an electrical code with a perfectly good valve
- 3. Cracked, split, or popped-off vacuum hose on systems that run vacuum control, so the valve never gets the signal it needs
- 4. Stuck or seized bypass valve mechanism, gummed up with carbon and oil so it won't move freely
- 5. Split diaphragm inside the valve assembly on older actuator-style setups, leaking and losing its ability to hold pressure
- 6. Boost pressure sensor feeding the ECU duff readings, making it think the valve isn't responding
- 7. ECM or boost controller fault, uncommon but it does happen
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read the codes and note anything stored alongside P0033, particularly P0299 underboost or other turbo control codes, as they point you straight at where the boost is going wrong
- 2. Get under the front end and check the connector at the solenoid or actuator for corrosion, bent pins, oil contamination, or a wire that's melted against the turbo housing
- 3. Inspect every vacuum hose and the intake pipework for splits, perished rubber, and loose clamps; a popped intercooler hose throws this code on a healthy system
- 4. Test the solenoid or actuator resistance against the manufacturer's figure and check it actually moves when commanded with a scan tool
- 5. Run a boost pressure test to see whether the engine is making the boost it should or falling short under load
- 6. Clear the code and road-test under proper load to confirm whether the fault comes back, which tells you if it's a dead component or an intermittent wiring fault
Common questions about P0033
What happens if I just keep driving with it like this? +
You'll spend most of your time in limp mode with the power chopped right back, which is annoying but won't strand you for short trips. The bigger risk is on the systems where the valve sticks shut and boost runs unregulated, because an overspeeding turbo can overheat and damage itself. If the power's already restricted, the ECU is doing its job protecting the engine. Don't ignore it for weeks though, get the boost control checked before a cheap solenoid turns into a turbo bill.
How quickly do I need to sort this out? +
It's not a roadside emergency in most cases, but it's not one to sit on either. If the car's gone into limp mode you should book it in within a few days, partly because driving around with no boost is miserable and partly because an uncontrolled wastegate or bypass valve can cook the turbo over time. If it only flickers up occasionally and clears, you've got a bit more breathing room, but it still wants diagnosing properly rather than just clearing the code and hoping.
Is it the valve itself that's gone, or is this a wiring problem? +
It can be either, and the only way to know is to test rather than guess. P0033 is an electrical circuit code, so it's just as likely to be a corroded connector, a chafed wire near the hot turbo, or a perished vacuum hose as it is a dead solenoid. Check the wiring and connectors first, they're cheap or free to fix. If the loom and the actuator both test fine to spec, then you're looking at the valve or solenoid itself, which on a typical UK family diesel runs a low to mid three-figure sum at an independent garage.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →