What does the P004A fault code mean?
The P004A fault code, applicable to all car manufacturers, means “Turbocharger/Supercharger Boost Control B Circuit/Open“.
Background information: A turbocharger uses the inertial force of exhaust gases from the engine to drive a turbine, which in turn drives a coaxial impeller to pressurize the intake air, thereby increasing the car’s power. A supercharger is an air compressor used to increase the intake air of an internal combustion engine. More intake air provides the engine with more oxygen, allowing the control module to deliver more fuel, thus increasing output power. The turbocharger/supercharger boost controller’s function is to, when the boost pressure reaches a set value, use air pressure to push a wastegate actuator (pneumatic mechanical type) to redirect some exhaust gases around the turbine, thereby reducing the turbine speed and controlling the boost level. This fault code indicates that the voltage in the turbocharger/supercharger boost control circuit is outside the calibrated normal range.
Symptoms of the P004A code may include:
- Insufficient boost causing decreased engine performance
- Overboost causing knocking and possible engine damage
- Engine malfunction light illuminated
Possible causes of the P004A code include:
- Boost pressure/turbocharger position sensor malfunction
- Turbocharger/supercharger malfunction
- Control solenoid valve malfunction
- Wiring problems
- Faulty PCM
- Vacuum leak if the valve is vacuum controlled
How to fix a P004A fault:
- Use an OBD scanner to diagnose the root cause of the problem and pinpoint the specific component causing the fault.
- Inspect the boost control circuit, wiring, and connectors for damage or corrosion. Repair or replace as needed.
- Test the boost control solenoid valve and boost pressure sensor for proper function. Replace if faulty.
- Inspect the turbocharger or supercharger for signs of damage or malfunction. Repair or replace if necessary.
- Clear the DTCs and test drive the vehicle to ensure the problem is resolved.
Vehicles Most Frequently Affected by Code P004A
This code appears on turbocharged and supercharged vehicles from multiple manufacturers, especially those using multi-stage or twin-turbo systems. Here are some frequently affected models: Engine & Transmission
- Volkswagen/Audi (2.0T, 3.0T, TDI engines)
- Ford (EcoBoost engines, F-150, Fusion, Escape)
- General Motors (Chevrolet Cruze, Malibu, Silver Lado 2.7T, Cadillac ATS/CTS)
- BMW (N54, N55, B58 turbocharged engines)
- Toyota/Lexus (supercharged or turbocharged versions)
- Hyundai/Kia (1.6T, 2.0T models)
Quick FAQs about Code P004A
Is it safe to drive with code P004A?
Limited. While many vehicles with the P004A code can be driven for short distances, prolonged use is not recommended. If boost control fails, the engine may run with reduced power or enter limp mode, making highway driving or overtaking dangerous. In some cases, unregulated boost can cause engine damage (rare). Diagnose and fix the problem as soon as possible to avoid further complications.
Will a dirty air filter or an intake leak trigger P004A?
No. P004A is strictly associated with the circuitry controlling the boost actuator, not the airflow sensor or hoses.
Will resetting the codes solve the problem?
Clearing the fault codes may temporarily turn off the engine malfunction indicator lamp, but if the underlying cause is not addressed, P004A will reappear.