P0033
Turbo Charger Bypass Valve Control CircuitP0033 is a generic OBD-II powertrain diagnostic trouble code: Turbo Charger Bypass Valve Control Circuit. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0033 means
P0033 — Turbocharger/Supercharger Bypass Valve Control Circuit — is a generic OBD-II code stored when the PCM detects that the control circuit for the turbo or supercharger bypass valve (also called a blow-off valve, recirculation valve, or anti-surge valve on turbo applications) is not operating within expected parameters. The code does not specify a direction (high or low) — it indicates a general circuit malfunction, which may include an open circuit, intermittent short, or a signal outside the plausible range in either direction.
The bypass valve is an electrically controlled solenoid (or solenoid-operated pneumatic valve) that diverts pressurised charge air back to the compressor inlet — or vents it to atmosphere — during throttle lift-off, preventing compressor surge. The ECM drives the solenoid via a PWM signal and monitors the circuit for correct impedance and response. A circuit fault means the PCM cannot confirm whether the valve is opening or closing as commanded.
On some platforms the same code also covers a supercharger bypass solenoid used to limit boost at low loads. Regardless of the induction type, a malfunctioning bypass valve can cause compressor surge, intercooler hose failures from pressure spikes, turbo bearing wear, and either overboosting or underboosting conditions depending on the valve's fail-safe position.
Common causes
Most-frequently reported root causes when P0033 is logged.
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1
Failed bypass valve solenoid coil — open or shorted winding causing the ECM to detect an out-of-range circuit.
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2
Broken, chafed, or corroded wiring in the solenoid control harness between ECM and the valve connector.
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3
Corroded or backed-out pins at the bypass valve electrical connector.
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4
Failed ECM/PCM driver circuit for the bypass valve output.
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5
Vacuum line disconnected, cracked, or collapsed on vacuum-operated bypass valves using a solenoid as pilot.
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6
Moisture or oil contamination inside the valve connector causing intermittent high resistance.
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7
Blown fuse or relay in the solenoid supply circuit.
Symptoms drivers notice
How to diagnose P0033
A typical diagnostic flow when this code is present.
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1
Retrieve all codes and note any companion boost pressure or MAP sensor codes that indicate secondary effects of the valve malfunction.
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2
Visually inspect the bypass valve solenoid connector, wiring harness, and nearby vacuum lines for damage, disconnection, or oil contamination.
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3
Measure solenoid coil resistance at the valve terminals; compare to the manufacturer specification — an open (OL) or shorted reading confirms internal solenoid failure.
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4
With the ignition ON, measure supply voltage at the connector; no voltage indicates a blown fuse, open relay, or broken supply wire.
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5
Check the control wire continuity from the ECM pin to the valve connector; a break indicates a harness fault.
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6
If electrically sound, apply direct 12 V to the solenoid (where safe per manufacturer guidance) and listen for valve actuation.
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7
Clear the code, perform a live-data boost-pressure road test, and confirm the bypass valve cycles correctly before closing the diagnosis.
Related powertrain codes
Frequently asked questions
What is the difference between P0033 and P0035?
P0033 is a generic circuit fault with no voltage direction specified. P0034 indicates the circuit is stuck low (short to ground or open coil). P0035 indicates the circuit is stuck high (short to battery voltage). Knowing the direction narrows the fault to a specific wiring failure mode.
Can a boost leak cause P0033?
A boost leak alone will not set P0033, which is a purely electrical circuit fault. However, a boost leak often coexists with a damaged bypass valve or hose, and both issues may be found together during the same repair.
Is P0033 exclusive to turbocharged engines?
No — the SAE definition covers supercharged engines as well. Some supercharger systems use an electrically controlled bypass valve to unload the blower at light throttle, and the same circuit monitoring logic applies.
How urgent is P0033 to repair?
It should be diagnosed promptly. If the valve is stuck closed, repeated compressor surge can accelerate turbo bearing and blade wear. If it is stuck open, boost will be lost and the engine may not achieve full power. Either condition risks secondary damage if left unaddressed.
Disabling P0033 in software
RaceTune can permanently disable P0033 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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