Dear e420A1
According to the information I have, there are two types of limp modes, see the following description for the two modes:

Electrical limp-home mode
In order to prevent damage to the automatic transmission in the event of an electrical fault, the gear currently engaged is held and the assigned diagnostic trouble code (DTC) is stored.

The limp-home mode comes into effect with the following procedure:


Stop vehicle.
Shift transmission selector lever to "P".
Shut off engine.
Wait at least 10 seconds .
Start engine.
After restarting engine, the vehicle can only be driven in 2nd or reverse gear.

NOTE: The engagement of "N -> D" and "N -> R" will be very harsh, since the electronic control of the automatic transmission has been turned off.
This type of limp-home mode can only reset by repairing the fault and erasing the DTCs with the Hand-Held Tester (HHT).

Mechanical-hydraulic limp-home mode
In order to prevent damage to the automatic transmission in the event of an mechanical-hydraulic fault,


the transmission shifts into 3rd gear and is held in this gear, or
the transmission shifts to the last "known good" gear and is held in that gear.
NOTE: This type of limp-home mode is reset by turning the Ignition OFF, and then ON again

It seems like your car goes into the Mechanical/Hydraulic limp mode, because you say it goes in third gear and can be re-set by simply turning your car on and off.

You are saying that your gear selector is at times difficult to move. As you probably know, there is no mechanical connection between the selector and the gearbox, the selector only actuates an electrical switch. The switch then tells the TCU which gear is selected and the TCU then energizes the appropriate solenoids to control the hydraulic flow in the transmission.

I would think that your shift lever problem is caused somewhere inside the console and is unrelated to your other problem.

My car is definitely in the electrical limp mode. The problem manifested itself both with the transmission and engine warm and cold.

The TCU is located under the hood, on the passenger side, close to the air intake under the windshield. If you stand in front of the car with the hood open, you can see a plastic cover, about 12x12 inches which is held down with 4 philips head screws. After removing the cover you will see a row of control units. The TCU is the second one from the bottom, it has two connectors on the top. I have attached a picture for you.
Once you have it out, you need to open the module, which you can do by sliding a two credit cards in between both sides of the housing and the connector base. I cleaned my board with a special PC board cleaner, which you can get at an electronics store. I also cleaned the wiring harness.


Dear C32AMG,

Thanks for your suggestions .The fluid is definitely gone from the TCM, and I have reset the codes with my generic scantool multiple times. The ones that keep coming back are the 0743 0753 0763 and 0758 codes. They all point towards problems with the solenoids. I have checked the resistance of the solenoids and they are in spec and I can actually hear all of them click when I power them externally.
You say you think that the 720 code which I had at the beginning is a likely cause, have you had this failure? and if so what did you do to solve it.
Thanks

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