BMW 740i Turbocharger Boost Sensor 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 monitor the amount of pressure in the system is needed. This is typically the boost pressure sensor, through a manifold absolute pressure sensor may be used instead or in addition.

When the turbocharger wastegate is closed, and there are no leaks in the system, the boost pressure solenoid will see a rise in boost pressure in the system, and this will be signalled to the engine control module (ECM) for further action. The same occurs for underboost conditions, and the ECM will work to correct the issue in the direction needed. This may be done by closing the wastegate, opening the wastegate, or alerting the driver there is an issue with the check engine light.

High or low engine power are common side effects of a failed boost pressure sensor. If the boost pressure sensor reports erroneously low boost pressure, the wastegate will close, high pressure will be introduced, and lean running conditions may be present. At higher engine speeds, this may result in lean running conditions. The opposite is true if the boost pressure sensor reports high boost pressures. The engine will lock power, and rch running conditions may be present. In all cases, the check engine light will illuminate and the ECM will store OBD codes related to these conditions.

The boost pressure sensor is yet another example of a sensor that can set the check engine light, and should not be ignored due to possible damage to the engine. Like any other time the check engine light is illuminated, the vehicle should be inspected and repaired immediately. Driving with a bad boost pressure solenoid can also lead to driveability issues, and these will further indicate that repair is needed.

Boost pressure sensors are not common points of failure, and the average sensor will last well over 100,000 miles. In fact, there are replacements of these sensors ranging into the 170,000 mile range for several vehicles. Unfortunately, there is no way to extend the life of the boost pressure sensor, but most will not require replacement in either case.

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. Most times, these sensors will be in working order, but they do fail at random, so they must be tested.

Boost pressure sensors are simply replaced by removing them from their mounting location, disconnecting the single electronic connector, and installing the new sensor. However, this may call for some components of the vehicle to be removed, as these are often placed in hard to reach areas.

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, but there are other components that may cause theses faults.

Many turbocharged engines will use only the manifold absolute pressure sensor instead of the boost pressure sensor. For this reason, it is very important to understand the entire turbocharger system before attempting repair.

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 or underboost condition, it may be more cost effective to have diagnosis performed. If the boost sensor is known to be faulty, replacement is a quick and easy job for the DIY mechanic when the sensor is in an easy to reach location.