BMW 428i Gran Coupe Turbocharger Boost Pressure Solenoid Replacement Cost

Turbocharged engines use air pressure created by the turbocharger to force air into the engine through the intake manifold. The amount of pressure that even a small turbocharger makes can exceed the factory specifications for intake pressure, so a component to regulate the amount of pressure in the system is needed. To vent overpressure, the boost pressure control solenoid is used to open the wastegate on demand from the engine computer. This may be a solenoid and valve combination, or a solenoid that allows air into a vacuum canister to open the wastegate.

The turbocharger boost pressure control solenoid is controlled by the engine management computer (ECM/PCM) and, depending on the manufacturer design, may open when the brakes are applied, the gas pedal is released, turbocharger speed becomes too low, or the boost pressure sensor detects overpressure. When the solenoid opens it allows the wastegate to open, sometimes indirectly, and boost pressure is vented into the exhaust pipe. Upon closing, the wastegate is pulled closed by the wastegate actuator, and the turbocharger will again build pressure in the system.

If the boost pressure control solenoid fails to operate, the check engine light will illuminate, especially under hard or sustained acceleration. However, if the vehicle is always driven very lightly, it may never have a reason to actuate, but this depends on the software for the particular vehicle. The engine may feel more powerful than normal on hard acceleration, but the check engine light will stay illuminated, and the vehicle may set itself into limp mode or safe mode. Lean running conditions may be detected at high engine speed, and these symptoms will be noted by OBD-II trouble codes stored in the ECM.

The boost pressure control solenoid should never be ignored. Not only will the closure of the wastegate cause the engine to run under extreme pressures, but the turbocharger will not be able to spool or slow efficiently. Also, overboost conditions in the intercooler piping and turbocharger compressor side may lead to boost leaks, and oil leaks may become evolve as time progresses. If the engine begins running lean as a result of the overboost situation, high heat will eventually cause the turbocharger and exhaust manifold to crack at the wastegate.

These solenoids live in a very hot environment and are in use constantly as the engine is running. That said, it is expected that they have a higher than normal failure rate, but they are fairly resilient. The average mileage of replacement for several vehicles is between 45,000 and 160,000 miles, so it is very difficult to understand when to expect this repair.

If the turbocharger wastegate is not functioning, the technician will begin by inspecting for play at the wastegate control rod, wastegate actuator, and visually inspecting the boost pressure control solenoid. This will allow the technician to eliminate simple and common failures. However, if everything i mechanically sound and the wastegate can be actuated by vacuum, the turbocharger boost pressure control solenoid will be tested using a diagnostic scanner to cause the wastegate to vent boost pressure. If the overboost situation is not alleviated, the manifold absolute pressure sensor and boost sensor will be tested prior to replacing the solenoid.

The boost pressure control solenoid can be replaced by removing fasteners and vacuum lines, plus the electronic connector for the boost pressure control solenoid. New clamps will be used when installing the new solenoid, and the solenoid will be tested once installed to ensure the wastegate opens successfully.

RepairPal recommends thorough testing of the turbocharger and boost control system before replacing parts associated with these systems. The OBD trouble codes found stored on the ECM or PCM will only alert the technician to which component detected the failure, not which component has failed. If overboost is detected, the boost pressure sensor or manifold absolute pressure sensor may be incorrect as well.

Not all turbocharged vehicles will use the boost pressure control solenoid. In fact, nearly all older vehicles with turbocharged engines will use pneumatic operations to open the wastegate. Also, vehicles with externally vented wastegates may have the solenoid placed in a remote location, so understanding the components of the turbocharging system in use is important.

This is a difficult diagnosis for anyone without a diagnostic scanner. It can be done, but it will be very difficult. Since most people without a professional scan tool will likely begin replacing parts to diagnose an overboost condition, it may be more cost effective to have diagnosis performed. If the solenoid is known to be faulty, replacement is a quick and easy job for the DIY mechanic.