My 2007 r320 CDI occasionally goes into limp mode. I have two codes that pop into my ECU. The first is p0299 Turbo underboost and the second is
p0401 exhaust gas recirculation flow insufficient detected. The most peculiar symptom is going into limp mode when making u-turns. I have seen other posts on this forum where individuals with the 642 diesel engine have had the same odd symptom. It will also randomly go into limp mode within the first three to five miles of driving after being started for the first time that day. After resetting the codes generally the car will drive without problems for the remainder of the day. Sometimes I can turn the car off, crank it back up, and it drives fine without remaining in limp mode. I drive extensively for work in this vehicle and sometimes will drive 3 to 500 Miles without an additional problem on a particular day. I have just turned two hundred thousand miles in the car and have had virtually no other problems with it since I've had it. Because the u-turn situation is so random I have not been able to get it to do this with my technician in the car and he is beginning to think I am crazy. However, the situation has occurred with many other people riding with me. can anyone offer me any insight into why the u turn situation is occurring because it makes no sense whatsoever. I have thoroughly cleaned the intake and EGR system with my motorvac diesel EGR cleaning machine. My EGR valve is spotless and appears to be functioning properly. I have been considering going ahead and replacing it just due to the mileage and the possibility that something else inside the EGR may be malfunctioning. Can anyone offer me any guidance or suggestions as to what this may be? Thank you very much in advance.

 

Could it be the exhaust pressure sensor? The one next to the egr valve.

As for happening when you are turning, maybe a wire is being stretched when you are turning causing it to lose contact?

 

was about to suggest same thing.

 

R-class.
Diesel.
200k miles.
Drive it to the nearest junkyard. Take the license plate off and walk away. Move on with your life.

 

I probably should have mentioned that my car is a Non Bluetec . With that being said would my system have the aforementioned exhaust gas pressure sensor? I have found OEM part numbers as well as the Bosch 10-digit part number but most of those mentioned it being a u42 system which seems to indicate or reference the DEF fluid heater system

 

Yes it does. A0071534328 - that might be an older part revision.

You will need a 23 or 24mm Spanner / google it. It’s a common problem.

Dont drop the metal washer when you take it off!

 

Thank you very much for your help. I do appreciate it

 

This. It's not going to get any better.