P0035
PowertrainTurbocharger/Supercharger Bypass Valve Control Circuit High
The ECU drives the turbo bypass valve solenoid through a control circuit, and it constantly watches the voltage on that wire. When it sees voltage sitting too high or detects a short to power, it logs P0035 and assumes something in that circuit has gone wrong. For you as the owner, that usually shows up as a power loss and a warning light, because the engine can't manage boost properly when it can't trust the valve it's trying to control.
ⓘ Information only. This page provides general educational information about fault code P0035. 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 P0035 mean?
P0035 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Turbocharger/Supercharger Bypass Valve Control Circuit High.
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 the dash, sometimes the only sign at first
- • Flat, sluggish acceleration, worst when you put your foot down on a slip road or hill
- • Car drops into limp mode and refuses to make full power until you restart it
- • Boost feels weak and the usual turbo spool you're used to hearing goes quiet
- • Slightly heavier fuel use because the engine is running a safe, inefficient map
- • Power delivery comes and goes, fine one minute and dead the next
Possible causes
Causes commonly associated with P0035, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Wiring fault in the bypass valve control circuit, a short to a positive feed or a chafed loom is the most common reason for a 'high' code
- 2. Damaged, corroded or half-seated connector at the solenoid, very common where the plug sits in the heat near the turbo
- 3. Failed solenoid or actuator with an open or shorted internal coil, so the ECU never sees the resistance it expects
- 4. Broken or high-resistance earth on the circuit, which fools the module into reading the line as high
- 5. Bypass valve itself stuck or stiff, dragging the whole circuit out of normal range
- 6. Faulty boost pressure sensor feeding bad numbers in, so the ECU misjudges what the valve should be doing
- 7. Failed driver inside the ECM or a calibration issue, rare, and only after everything else checks out
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 all stored codes first, not just P0035. Wiring or boost codes alongside it (P0234, P0299) tell you whether you're chasing an electrical fault or a mechanical boost problem.
- 2. Get to the solenoid connector and inspect it properly. Unplug it, check for green corrosion, spread pins or oil ingress, and wiggle the loom where it runs near the hot side of the turbo.
- 3. Measure the solenoid resistance across its terminals against the workshop spec, typically a few ohms to low tens of ohms depending on the engine. Open or shorted means the valve is the fault.
- 4. Back-probe the control wire with a multimeter, key on, and look for a short to battery voltage or a damaged feed. This is what the 'high' in the code is pointing at.
- 5. Confirm the earth side is clean and low resistance, because a bad earth throws false high readings.
- 6. Clear the code and road test under load. If it comes straight back, the fault is live and not a one-off glitch.
Common questions about P0035
How do I know if it's the wiring, the valve, or a sensor on my car? +
Work from cheapest to dearest. Start at the connector, because a corroded or oily plug near the turbo causes a big share of these and costs nothing to clean and reseat. If that's clean, ohm out the solenoid against the spec, an open or short there means the valve is dead. If the solenoid reads fine and the wiring is sound, then look at whether the boost sensor is feeding rubbish numbers. A 'high' code almost always points at the electrical side first, so don't condemn the turbo before you've checked the wire and the earth.
Can I sort this myself or does it need a garage? +
Some of it, yes. Cleaning the connector, reseating the plug, or repairing a single chafed wire is well within reach if you can find the loom and you've got a multimeter. Replacing the bypass solenoid is often straightforward on petrol turbos where it's bolted to the intake. What pushes it into garage territory is tracing an intermittent short or anything that means disturbing the turbo plumbing, plus you'll want the code confirmed gone under a proper road test. Parts are usually modest, the solenoid itself is often £30 to £120, it's the diagnosis time that adds up.
If I just clear the code, will it stay gone? +
Only if the fault was a genuine one-off, which is rare with a circuit code like this. Clear it and the light typically returns within a drive or two, often the moment the engine demands boost and the ECU rechecks the circuit. Clearing the code is useful as a test to see if the fault is live, not as a fix. If it comes back fast, you've still got the original problem.
What's the risk if I just keep driving on it? +
You won't blow the engine up overnight, but you're driving a car that keeps dropping into limp mode and can't control its boost properly. If the bypass valve is stuck or the wiring is shorting at the wrong moment, you can get overboost or wild boost spikes that hammer the turbo over time. Best case you're stuck with no power and worse fuel economy. Worst case a cheap connector fix turns into a turbo that's been stressed for months. Get it looked at before a quick repair becomes an expensive one.
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 →