"Boost control A" 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. The letters A and B denote two separate actuators, for example on the low- and high-pressure turbocharger of a two-stage system, not the cylinder banks. 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.
Medium severity. Can I keep driving?Drive without demanding power and go to a repair shop soon. If you see a lot of blue smoke or hear a metallic noise, shut off the engine.
Symptoms
- Check engine light on, sometimes only intermittently
- Loss of power or reduced power mode
- Sudden, jerky loss of power
- Overboost possible in rare cases
Most likely causes
- Loose contact at the actuator connector
- Wire broken internally by engine movement
- Corroded terminals
- Actuator itself faulty
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It can trigger limp mode.
- It affects emissions.
What each character of P004E means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 0: Subsystem depends on the code range
- 4E: Specific fault in that system
Frequently asked questions
Can I keep driving with code P004E?
Drive without demanding power and go to a repair shop soon. If you see a lot of blue smoke or hear a metallic noise, shut off the engine.
What causes code P004E?
The most common causes are: loose contact at the actuator connector; wire broken internally by engine movement; corroded terminals.
Related codes
- P0045Turbocharger/Supercharger Boost Control A Circuit/Open
- P0046Turbocharger/Supercharger Boost Control A Circuit Range/Performance
- P0047Turbocharger/Supercharger Boost Control A Circuit Low
- P0048Turbocharger/Supercharger Boost Control A Circuit High
- P004FTurbocharger/Supercharger Boost Control B Circuit Intermittent/Erratic
Sources
- law.cornell.edu: 13 CCR 1968.2
- en.wikipedia.org: Boost controller
- en.wikipedia.org: Variable geometry turbocharger
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.