P004B code meaning
Turbocharger/Supercharger Boost Control B Circuit Range/Performance
Powertrain system Generic code P00xx codes Check engine light
What P004B means
"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.
P004B at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 4 hours
- Clears after repairAfter a drive cycle
Symptoms of P004B
- Check engine light on
- Loss of power or reduced power mode
- Weak acceleration, noticeable turbo lag
- Overboost possible in rare cases
Common causes of P004B
- Most likelyTurbine vanes or wastegate linkage sooted or sticking
- Most likelyElectric actuator faulty
- PossibleActuator learn value invalid, e.g. after low battery voltage at start
- PossibleVacuum leak at a pneumatic actuator
- Less likelyActuator position sensor faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Boost control actuator bTurbochargerActuator position sensor
What each part of P004B means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 0 | Area: fuel and air metering and auxiliary emission controls. |
| 4B | The exact fault in that area. |
What to do next
- Note P004B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P004B
What does P004B mean?
P004B means "Turbocharger/Supercharger Boost Control B Circuit Range/Performance". "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. It is a generic code, so it means the same on every make.
Is it safe to drive with P004B?
Drive gently and only to a workshop. With P004B the car can go into limp mode (reduced power) to protect itself.
Will P004B fail an emissions test?
Yes, it can. P004B is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P004B to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P004B clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.