Turbo Charger Bypass Valve Control Circuit
Diagnostic trouble code P0033 indicates a malfunction in the electrical circuit controlling the turbocharger or supercharger bypass valve. The engine control module (ECM) sets this code when it detects an open, short, or out-of-range voltage condition in the bypass valve control circuit.
While the vehicle can usually still be driven, a malfunctioning bypass valve can lead to poor engine performance, reduced fuel economy, and potential long-term damage to the turbocharger due to compressor surge.
Common symptoms
- Illuminated Check Engine Light
- Lack of engine power or poor acceleration
- Fluttering or surging noises from the turbocharger
- Decreased fuel efficiency
- Engine hesitation during acceleration
Likely causes
- Faulty turbocharger bypass valve (blow-off valve)
- Damaged, corroded, or loose wiring and connectors in the bypass valve circuit
- Vacuum leak in the lines controlling the bypass valve (if vacuum-actuated)
- Failed bypass valve control solenoid
- Faulty Engine Control Module (ECM) (rare)
What to check before replacing parts
Visually inspect the wiring and connectors for the turbocharger bypass valve control solenoid.
Look for: Look for frayed wires, melted insulation, corroded pins, or loose connections that could cause an open or short circuit.
Check the vacuum lines connected to the bypass valve and control solenoid (if applicable).
Look for: Inspect for cracked, disconnected, or collapsed vacuum hoses that would prevent the valve from operating properly.
Test the resistance of the bypass valve control solenoid using a digital multimeter.
Look for: Compare the measured resistance to the manufacturer's specifications. An infinite reading indicates an open circuit, while a reading of zero indicates a short.
Check for proper voltage and ground at the bypass valve control solenoid connector with the key on, engine off.
Look for: You should see battery voltage on the power feed circuit and a good ground or ECM-switched ground on the control circuit. Lack of voltage indicates a wiring or fuse issue.
Command the bypass valve solenoid on and off using a bi-directional scan tool.
Look for: Listen for an audible click from the solenoid and verify vacuum/pressure changes. If the solenoid does not click despite having good power and ground, the solenoid itself is likely faulty.
This page explains the generic P0033 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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