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

P004A Turbocharger/Supercharger Boost Control B Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

"Boost control B" is the electrically driven actuator the engine control module uses to set boost pressure: depending on the engine a pulse-width modulated solenoid or vacuum converter at the wastegate, the control valve of variable turbine vanes, or an electric actuator with position feedback. B is the second actuator, for example on the high-pressure turbocharger of a two-stage system or on the second turbocharger; it does not denote cylinder bank 2. This code is set when the control circuit is open: with the driver switched off no load can be measured, or the measured state does not match the command. Without control the actuator usually falls back to its rest position, which on most engines means low boost; depending on the design too much boost is also possible.

Likely causes

Connector at the actuator corroded or loose
Wire broken or chafed through
Solenoid coil in the actuator burnt out
Fuse or ignition supply faulty
Engine control module or separate actuator control unit faulty

Symptoms

  • Check engine light on
  • Loss of power or reduced power mode
  • Weak acceleration, noticeable turbo lag
  • Overboost possible in rare cases

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–900
Time0.5–2.5 h

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

Parts involved

boost control actuator bboost control actuator wiringengine control module

Related codes

P004BP004CP004DP004FP005EP0045

References: law.cornell.edu, en.wikipedia.org, en.wikipedia.org.