Powertrain, generic · Fuel and air metering, auxiliary emission controls

P0034 Turbocharger/Supercharger Bypass Valve A Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

The turbocharger bypass valve A is the compressor recirculation (diverter) valve: it connects the pressure side of the compressor with the intake side upstream of the turbocharger. It opens when the throttle closes quickly at high boost, so the compressor does not surge and the compressor wheel keeps its speed for the next acceleration. It is not the wastegate, which bypasses exhaust gas around the turbine and has its own codes. The valve is either electric or a vacuum unit controlled by a solenoid. P0034 means the voltage at the control output is too low, typically because the control wire is shorted to ground; on some control modules an open circuit also sets this code.

Likely causes

Control wire shorted to ground
Valve shorted internally
Supply missing, e.g. fuse or main relay
Output driver in the engine control module faulty

Symptoms

  • Check engine light on
  • Fluttering or hissing when lifting off the throttle if the valve stays closed
  • Weak response after gear changes
  • Too little boost if the valve stays open

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–350
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

turbocharger bypass valveturbocharger bypass valve wiringengine control module

Related codes

P0033P0035P0039P2261P00C1

References: law.cornell.edu, gsi.ext.gm.com, saabwisonline.com, ms-motorservice.com.