P004A code meaning
Turbocharger/Supercharger Boost Control B Circuit/Open
Powertrain system Generic code P00xx codes Check engine light
What P004A 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. 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.
P004A at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P004A
- Check engine light on
- Loss of power or reduced power mode
- Weak acceleration, noticeable turbo lag
- Overboost possible in rare cases
Common causes of P004A
- Most likelyConnector at the actuator corroded or loose
- Most likelyWire broken or chafed through
- PossibleSolenoid coil in the actuator burnt out
- PossibleFuse or ignition supply faulty
- Less likelyEngine control module or separate actuator control unit 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 bBoost control actuator wiringEngine control module
What each part of P004A 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. |
| 4A | The exact fault in that area. |
What to do next
- Note P004A 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 P004A
What does P004A mean?
P004A means "Turbocharger/Supercharger Boost Control B Circuit/Open". "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 P004A?
Drive gently and only to a workshop. With P004A the car can go into limp mode (reduced power) to protect itself.
Will P004A fail an emissions test?
Yes, it can. P004A 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 P004A to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P004A 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.