P003B
Turbocharger/Supercharger Boost Control B Position Exceeded Learning Limit.
- 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
- 3B
- FaultThe specific fault in that area
What it means
P003B is a generic code meaning the position of the 'B' boost control actuator (the second turbocharger or supercharger boost control, such as a wastegate or variable geometry vane actuator) has moved beyond the limit the control unit can learn or adapt to. The engine control unit compares the actuator's commanded and actual position against stored learned values, and has seen the correction needed exceed the permitted range. Which turbocharger or bank 'B' refers to depends on the engine and model.
Symptoms
- Engine warning light on
- Loss of power or reduced boost, often with the engine in limp mode
- Turbo lag or sluggish acceleration
- Overboost or erratic boost delivery
- Whistling, rattling or unusual turbo noises
- Poorer fuel economy
Possible causes
- Sticking or seized boost control actuator, wastegate or variable vane mechanism caused by carbon build-up or wearlikely
- Faulty electric or vacuum-operated boost actuator, or a failed position sensor within itlikely
- Damaged, corroded or loose wiring and connectors to the actuator or position sensorpossible
- Vacuum leak, split hose or faulty solenoid on a vacuum-operated actuatorpossible
- Boost leak or restriction in the intake or charge air system affecting the boost controlpossible
- Worn turbocharger or linkage, or actuator moved out of adjustment after a previous repairpossible
- Outdated control unit software or learned values not reset after turbo or actuator replacementrare
How to diagnose
- Read all stored and pending codes and note the freeze frame data, such as engine load, speed and boost at the time of the fault
- Check for related codes covering boost pressure, actuator circuits, sensors or the other turbo, and follow the manufacturer's information for the model
- Visually inspect the actuator, linkage, wiring and connectors for damage, corrosion, heat damage or looseness
- Inspect vacuum hoses, solenoid and charge air pipes for splits, leaks, loose clamps or oil contamination
- Check the actuator moves freely through its full range by hand or with a vacuum pump where applicable, and look for binding or carbon build-up
- Use a scan tool to command the actuator and compare commanded versus actual position and boost on a live data graph
- Check actuator supply voltage, earth and signal circuits with a multimeter against the manufacturer's specification
- Check for available software updates for the engine control unit and whether an adaptation or learning procedure is required
How to fix
- Clean or free off a sticking wastegate or vane mechanism, or replace the turbocharger if it is worn or seized
- Replace a faulty boost actuator or its position sensor, then carry out the adaptation procedure specified for the model
- Repair or replace damaged wiring, terminals or connectors
- Replace split or leaking vacuum hoses, faulty solenoids or boost leaks in the charge air system
- Carry out the manufacturer's actuator learning or reset procedure after repairs, and apply a control unit software update if a known fault exists for the vehicle
Can I keep driving?
The car can usually be driven carefully for a short time, but the engine may be in limp mode with reduced power. Get it checked soon, as persistent over- or under-boost can damage the turbo or engine.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.