What it means
The control circuit for turbocharger or supercharger boost control B is open or has a malfunction.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
Boost Control B is a separate boost-control circuit used by some turbocharger or supercharger systems to operate an actuator or solenoid. The module checks whether this circuit can carry out its commanded function. P004A sets when the Boost Control B circuit is open or malfunctioning, for example from a broken wire, a backed-out pin, or a failed internal connection.
Common causes
Most likely first.
- Wiring break
- Pin pushed back out of connector body
- Cracked solder joint inside the module or sensor
Symptoms
- Check engine light on
- Reduced engine performance
How to diagnose it
- Review freeze-frame data and live boost-control readings to identify when Boost Control B stopped responding.
- Locate the Boost Control B component from the vehicle wiring diagram and inspect its connector and harness for a break, disconnection, heat damage, or backed-out pin.
- Check the Boost Control B circuit's power, ground, and control wiring for an open using the manufacturer's procedure.
- Test the actuator or solenoid circuit for continuity and inspect any module or sensor connector implicated by the wiring diagram.
- If the circuit and component pass, verify module command and feedback with the manufacturer's diagnostic procedure.
Common fixes
- Reconnect a loose Boost Control B connector and secure its harness.
- Repair a broken wire or backed-out pin in the Boost Control B circuit.
- Replace the Boost Control B actuator or solenoid if its internal circuit is confirmed open.
- Repair a verified internal connection or module-control fault after testing localizes it.
Can I keep driving?
Reduced power or limp mode may occur, so avoid towing, hard acceleration, and traffic situations that require quick acceleration until the Boost Control B circuit is diagnosed. Stop safely if there is a sudden loss of power, smoke, or unusual turbo noise.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.