Hello, I have a 2002 W210 e320 4matic Wagon with a problem. Whenever I engage the kickdown switch the car is immediately sent into limp mode until I turn off the ignition and restart and it immediately returns to normal.

I have replaced the throttle positions sensor, so I don't believe that is the problem. Next I'm suspecting I need to replace the kickdown switch, but I'm wondering if there is a relay which the kickdown switch activates that should be tested first.

The code that is pushed when this happens is P0123.

Any suggestions on what this may be, if there is a relay and its location, and how to replace the kickdown switch behind the gas pedal would be appreciated.