Mercedes Diesel Engine Turbo Code Repair

Mechanics Hub - June 9, 2014
Turbo Boost Performance Code Mercedes Diesel Engine

The “turbo boost performance” code is the fussiest one of all with Mercedes MBE 900 diesel engines. It involves several different checks on the sensors, EGR, intake throttle among other basic checks. When I see an engine with this code I know it's going to cost us a lot of time and parts depending what the specific failure is.

The very first check is the boost sensor which signals the engine control unit that the boost is in the sweet spot. If not the check engine light will come on guaranteed. The main problem with these sensors is the coot build up on the sensor. The soot does not allow the sensor to provide an accurate reading. Once it sends a signal out to left field we get an amber light on the dash.

Another check is the intake throttle valve which can be tested using the diagnostic software on the laptop (mandatory equipment). You can send a command to make it open at a certain percentage to see if it's positioning itself correctly. This valve is used to heat up the engine for parked regenerations.

The EGR has to be checked out as well using the same procedure as the intake throttle valve. Using the software you can command the EGR motor to open and close at a specified position. If it does not give an accurate result replacement is in order. The EGR gets a lot of soot and ash flowing through it daily so this will cause a build up and eventually the valve will stick and cause an engine code and loss of power.

In the video you will see a coolant leak we are attending to that is on the turbo side behind the exhaust manifold. The problem is a steel coolant line that cools the “doser valve” (shoots fuel into the exhaust system during regenerations). It's in a tight spot so getting to it will take some work. The line is all steel for obvious reasons... to resist the high heat generated by the exhaust system. That much heat would disintegrate a rubber coolant hose.

All these jobs have been completed and the coolant leak has been repaired since this video was produced but the engine code is still popping up once in a while. The EGR and boost pressure sensor has been replaced. It's not common to have coincidental codes acting up at the same time. Once one code is repaired another scan with the diagnostic software will tell us if there is another code lurking or everything is cleared up.
Diesel Engines