P004A
Turbocharger/Supercharger Boost Control B Circuit/Open.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 0
- AreaFuel and air metering, auxiliary emission controls
- 4A
- FaultThe specific fault in that area
What it means
P004A is the generic code for an open circuit or circuit fault in the 'B' turbocharger or supercharger boost control circuit. The engine control unit monitors the driver circuit that operates the boost control device, such as a wastegate or variable geometry actuator solenoid, and has seen a voltage or current that does not match what it commanded. Which device counts as 'B' depends on the engine and the manufacturer's layout, so check the model-specific information.
Symptoms
- Engine warning light on
- Loss of power or limp mode
- Boost pressure lower or higher than expected
- Turbo not building boost or surging
- Poor acceleration and sluggish response
- Possible increased fuel consumption
Possible causes
- Damaged, chafed or corroded wiring to the boost control solenoid or actuator, including an open circuitlikely
- Poor connection or corroded or loose terminals at the actuator or solenoid connectorlikely
- Faulty boost control solenoid, wastegate actuator or electronic turbo actuator with an open internal windinglikely
- Heat damage to wiring or connector near the turbocharger or exhaustpossible
- Blown fuse or faulty relay or power supply to the boost control circuit (depends on the model)possible
- Fault in the engine control unit output driverrare
- Outdated control unit software where the manufacturer has documented a known faultrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting engine load, speed and temperature when the fault set.
- Check for related codes such as boost pressure, actuator position or turbo performance faults, and work out which device the 'B' circuit refers to on this model using the manufacturer's information.
- Visually inspect the wiring, connector and vacuum or hose routing at the boost control device for chafing, heat damage, oil contamination, corrosion or looseness.
- Check the relevant fuse and relay and confirm the supply voltage and earth at the connector with the ignition on.
- Measure the resistance of the solenoid or actuator against the specification for the model, and check the wiring for continuity and shorts to earth or supply.
- Use a scan tool to operate the actuator and confirm it responds, and watch the commanded versus actual boost or position.
- Check for mechanical problems such as a stuck wastegate or vanes, and for boost leaks, once the electrical circuit tests good.
- Check whether the manufacturer has published a software update for the fault, and clear the codes and road test to confirm the repair.
How to fix
- Repair or replace damaged wiring and fix any open circuit, using proper soldered or sealed repairs.
- Clean, repair or replace corroded or loose connectors and terminals.
- Replace the faulty boost control solenoid or actuator, and adapt or calibrate it if the model requires it.
- Replace the blown fuse or faulty relay after finding the cause of the failure.
- Update the control unit software if an outdated calibration is a documented cause, or replace the control unit only after all other causes are ruled out.
Can I keep driving?
The car can usually be driven gently for a short time, but it will probably have reduced power and may be in limp mode. Get it checked soon, as running with incorrect boost can lead to further faults or engine and turbo damage.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.