Fault code P0034 – turbo charger bypass valve control circuit low

Fault code P0034 is called “Turbo Charger Bypass Valve Control Circuit Low” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0034

OBD-II fault code P0034 is a generic fault code defined as “low signal level in turbocharger bypass valve control circuit”. It is set when the Powertrain Control Module (PCM) detects a fault in the bypass valve control circuit.

The electronically controlled bypass valve is designed to relieve the overpressure of the turbocharger. In most cars it is actuated by a small electric motor, a vacuum actuator is rare.

Electronic valves are controlled directly by a voltage signal from the PCM, and with a vacuum actuator by a vacuum control solenoid. The vacuum control solenoid is normally supplied with a constant vacuum.

The voltage signal from the PCM initiates opening or closing of the solenoid to provide or limit vacuum to the valve as required.

Electronically controlled turbocharger bypass valves are monitored through the PCM signal circuit. If the signal voltage is below the programmed range for an unacceptable time, error code P0034 will be stored.

Symptoms of vehicle malfunctions

The main signal that an error P0034 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

1. The “Check engine” control lamp on the control panel will light up (the code will be memorized as a fault).
2. Other related fault codes may also be present.
3. Random noises from turbocharger bypass valve or hoses.
4. Elevated engine or transmission temperature.
5. Detonation in cylinders due to high temperatures.
6. Spark plugs may be dirty.
7. Reduced engine performance.
8. Black smoke coming from the exhaust pipe.

Error P0034 is considered serious because the conditions that cause this code to persist can cause serious engine damage. Due to excessive or insufficient turbocharger boost pressure.

Factors that can cause this error code

The error code P0034 can mean that one or more of the following problems have occurred:

• Defective boost pressure sensor.
• Turbocharger bypass valve is defective.
• Problems with turbocharger bypass valve actuator.
• Loose, corroded or disconnected electrical wires in the turbocharger bypass valve control sensor circuit.
• Worn or disconnected vacuum lines (for vacuum actuated bypass valves).
• Sometimes faulty PCM module is the cause.

How to fix or reset OBD-2 code P0034

Some suggested steps for troubleshooting and fix the error code P0034:

1. Read all stored data and error codes with an OBD-II scanner.
2. Clear the error codes from the vehicle’s computer memory.
3. Test-drive the vehicle to see if code P0034 appears again.
4. Perform a visual inspection and repair or replace damaged electrical wiring if necessary.
5. Check the turbocharger bypass valve as well as the boost pressure sensor.
6. If there is a problem with the PCM, reprogram or replace the control module.

Diagnose and repair of problems

Before you begin the process of troubleshooting P0034, you should research the technical service bulletins (TSBs) for your particular vehicle. In some cases, this can save you a lot of time by pointing you in the right direction.

Next, you should read any stored trouble codes, then erase from memory and test drive. If the code is back, continue testing the components.

Check the turbocharger bypass valve

Disconnect the supercharger solenoid valve and remove it from the vehicle. Apply air to the intake end, the valve should allow air to pass at rest. If air does not flow, the charge solenoid may be blocked or wedged and must be replaced.

Check valve operation with a power supply. Connect 12 volts to the positive side of the solenoid, then connect the ground wire to the negative side of the solenoid.

There will be an audible click, indicating that the solenoid is switching. Disconnect and reconnect the power supply several times to verify that the solenoid is switching consistently.

As long as the wires are connected to the bypass valve, purge it again, no air should be passing through. If air is passing, replace the boost solenoid.

Check charge bypass valve wiring

Any problem with the turbocharger bypass valve wiring will generate code P0034. You can use a multimeter to check the continuity of the circuit, or you can use a test lamp.

Since the entire supercharger solenoid circuit is under the hood of the vehicle, check for moisture and corrosion on the connectors and along the wiring.

If defective wires are found during the inspection, they must be replaced, the same goes for the connectors. When checking the wiring harness for shorts, do a poke test along each wire.

On which vehicles does this problem occur most frequently

Fault code P0034 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

• Audi
• Chevrolet (Cruze)
• Dodge
• Ford
• Honda (Accord)
• Lexus (RX300)
• Mazda (CX-5)
• Mercedes-Benz
• Nissan
• Opel
• Peugeot (308)
• Pontiac
• Saab
• Subaru
• Toyota
• Volkswagen

Fault code P0034 can sometimes be found with other errors. The most common are the following: P0016, P0031, P0033, P0035, P0051, P0500.

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