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

P004B Turbocharger/Supercharger Boost Control B Circuit Range/Performance

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. With this code the circuit is electrically intact, but the actuator does not follow the command plausibly: its actual position deviates too far or too long from the target, or its learned values do not fit. Boost is then too low or too high depending on where it sticks, often with reduced power.

Likely causes

Turbine vanes or wastegate linkage sooted or sticking
Electric actuator faulty
Actuator learn value invalid, e.g. after low battery voltage at start
Vacuum leak at a pneumatic actuator
Actuator position sensor 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

DifficultyHardWorkshop job
Parts and labour€0–3,000
Time0.5–4 h

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

Parts involved

boost control actuator bturbochargeractuator position sensor

Related codes

P004AP004CP004DP003BP0046

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