P004BTurbocharger/Supercharger Boost Control B Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- "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.
- What you may notice
- Check engine light on
- Loss of power or reduced power mode
- Weak acceleration, noticeable turbo lag
- Overboost possible in rare cases
- Likely causes
- LikelyTurbine vanes or wastegate linkage sooted or sticking
- LikelyElectric actuator faulty
- PossibleActuator learn value invalid, e.g. after low battery voltage at start
- PossibleVacuum leak at a pneumatic actuator
- RareActuator position sensor faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €0 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.