The OP said "Limp Home Mode" which is a specific MB name for the condition indicating they understand what's happening.

Actually in a CAN based car like the E320 it's the ECU which sets the parameters for 'restricted operation'. It's never the engine or transmission. They just do what they're told.

After reading the OP’s original post, it was clear to me that he was using the “limp home mode” term generically. As far as his understanding what’s happening with his car, the fact that he spent $400 bucks to replace the MAF sensor because someone said “that could be the problem”, tells me that he doesn’t know what’s happening. That’s why he’s asking for help, which is what we’re trying to do.



It’s never the engine or transmission??? I’m not sure I understand this.

Which ECU are you referring to that “sets the parameters” for restricted operation? Threads like this prove my point that most people simply don’t understand what “limp mode” really means.

Let me explain. The transmission ECU looks at the internal speed sensors, and gearshift recognition, etc., to determine when to intervene via “limp mode”. As you posted previously, this is to prevent unnecessary damage. When the transmission goes into “limp mode”, you’ll have a very harsh engagement when shifting into R or D, and, as you correctly stated, the transmission will be stuck in 2nd gear. The Check Engine light will come on as well. The reason for the Check Engine light is because there isn’t any “Check Transmission” warning light! If the car were scanned for fault codes in this condition, the engine ECU would simply say to check for fault codes in the transmission ECU.

The engine ECU, (in this case either ME-SFI 2.0 or 2.8), or the traction system ECU determines when throttle control intervention is necessary, via “limp mode”, and again results in the Check Engine light or the ESP warning light being illuminated. This variant of “limp mode” is far less common on MB vehicles.

Now, back to quan1’s problem. What’s your car doing?