This customer had a BMW 1 Series with a B38 engine that was in limp mode. After the oil cooler was repaired, the car went into limp mode because the turbo wastegate was out of adjustment. A specific cause is not known in this case. The actuator can sometimes become misaligned during repairs to the coolant system if there are still air bubbles in the system. Or, of course, when a new turbo is installed. The garage tried to clear the error codes, but this was unsuccessful. They then tried to recalibrate the wastegate, but this also failed. Many calibrations require specific dealer software to obtain a more detailed problem description and to unlock the functions for calibrating certain parts. BimmerStore was therefore called in to solve this problem.
After reading the error codes, we could see that the wastegate was unable to find the closed position. The electronically controlled wastegates in BMWs are automatically recalibrated by the car itself every time you start the engine. This is to ensure that your driving experience is optimal. When you start the car and it tries to find the start and end positions of the wastegate but cannot find one of these two points, your car will lose turbo pressure, go into limp mode, and display error messages. The error messages only appear when there is more than 2 mm of play on the actuator rod. Tolerances within 2 mm do not trigger error messages.
In this case, there was play on the actuator rod, preventing the wastegate from finding the closed position. In that case, the rod must be lengthened. Some examples of error codes you may encounter are 123401, 123412, 123432, 123437, and 123701. This occurs when the closed position cannot be found. It is also possible that it cannot find the open position. In principle, the repair method is the same.
After testing the wastegate, we receive a message that it is +3.20 mm too short. It is therefore also possible that yours is -3.20 mm if it cannot find the open position. In that case, the rod must be shortened. In general, you can calculate that 1 rotation of the nut on the rod removes 1 mm of play. In this case, we need to loosen the rod and turn the bolt on the rod 3 rotations to lengthen the rod and eliminate the play.
In principle, your car will no longer give an error message or go into limp mode if you stay within the 2 mm tolerance. However, for maximum engine performance, it is best if there is no play on the wastegate at all. The closer you are to the 0.00 mm tolerance, the better. After correcting the rod, we recalibrated the wastegate and successfully removed the error codes. This was a simple repair. However, the original dealer said that the turbo would have to be replaced to solve the problem. By calling in an independent BMW specialist, this customer saved thousands of euros!
Another reason why this error code may occur is the wiring harness. In the B38 and B48 engines, the wiring harnesses sometimes overheat or experience EMC interference, which can cause the error code to appear.
BMW is already aware of this problem and has released an improved wiring harness. The part number has remained the same, but it has been given a higher index number, which indicates that it is a new version of the same part. In this new wiring harness, the wires are twisted, providing better protection against EMC interference. So, do you have a B38 or B48 engine and is your actuator still working properly? Did the problem originally occur when it was hot, or does it always recur when it's hot? And do you still have an old wiring harness where the wires are not twisted? If so, this might be the source of your problem.
Loose wastegate valve (mechanical defect)
In some cases, the problem is not electrical or electronic, but purely mechanical. The wastegate valve itself can become detached from the valve rod or the seat in the turbine housing. This prevents the valve from closing properly and causes turbo pressure to escape, even if the actuator is working correctly. The photos above clearly show that the old turbo has a valve that is crooked in the seat, while the new turbo has a perfectly flat seal.
A loose or deformed wastegate valve can also cause rattling noises when the engine is cold or idling (“wastegate rattle”) and ultimately leads to permanent power loss and error codes relating to turbo pressure control. In such cases, adjusting the actuator rod will no longer help — the only lasting solution is to overhaul or replace the turbo.
BMW fault codes 123401, 123412, 123432, 123437, ... - Turbo wastegate actuator malfunction