P004FTurbocharger/Supercharger Boost Control B Circuit Intermittent/Erratic
- 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. This code is set when the circuit signal drops out briefly or jumps, as with a loose contact. Boost then fluctuates and reduced power may occur only now and then. 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.
- What you may notice
- Check engine light on, sometimes only intermittently
- Loss of power or reduced power mode
- Sudden, jerky loss of power
- Overboost possible in rare cases
- Likely causes
- LikelyLoose contact at the actuator connector
- LikelyWire broken internally by engine movement
- PossibleCorroded terminals
- RareActuator itself faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €50 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.