Fuel and air

P0034 — Turbo/Supercharger Bypass Valve Control Circuit Low

Severity: medium Drive with care, to a shop

What P0034 means

The engine control module operates an electric bypass (recirculation) valve that relieves excess boost pressure when the throttle closes. P0034 sets when the module sees a voltage in the valve's control circuit lower than expected, usually from a short to ground or a faulty valve. Boost control may then be inaccurate.

Symptoms

  • Check Engine light on
  • Reduced power and sluggish acceleration
  • Low boost or turbo lag
  • Whistling, fluttering or other odd noises from the turbo
  • Intermittent loss of boost
  • Limp mode activation

Possible causes

  1. Failed bypass valve or its solenoid actuator
  2. Short to ground in the control wiring
  3. Open circuit, corroded terminals or high resistance in the harness or connector
  4. Poor ground or missing power supply to the valve
  5. Faulty wastegate control valve if it shares the circuit
  6. Failed engine control module (uncommon)

How to diagnose

  1. Scan all codes and freeze frame data, clear the code and see if it returns
  2. Inspect the valve connector and harness for chafing, melting, oil, moisture and corroded pins
  3. Check for power and ground at the valve connector with a multimeter
  4. Measure the valve coil resistance and compare it to the spec for your vehicle
  5. Test the control wire for a short to ground and for continuity back to the module
  6. Command the valve with a scan tool and listen for it clicking
  7. Inspect the valve's vacuum or air hoses for cracks and leaks
  8. If the circuit tests good, consider the control module last

Common fixes

  • Replace the bypass valve or its actuator
  • Repair or replace the damaged wiring and connector
  • Restore the missing power or ground to the circuit
  • Replace or reprogram the control module if it is confirmed faulty

Questions and answers

What does P0034 mean?

It means the control circuit of the turbo or supercharger bypass valve is reading low voltage. The cause is usually a short to ground or a bad valve.

Can I drive with code P0034?

Briefly and carefully, for example to a shop. You may lose power, and extended driving can put extra strain on the turbo, so don't put off the diagnosis.

How do I fix P0034?

Start with the wiring and connector at the valve, then check power, ground and the valve's resistance. Most often the fix is a wiring repair or a new valve, and the control module is rarely at fault.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.