Originally Posted by emmotto

I have a 2012 C300 4matic sedan with KG. The car is new - bought at the end of the model year in late August 2012 - total mileage 1956 - 400+ of which have been put on by the dealer.

I began developing intermittent KG problems in November, slowly increasing in frequency to the point where is was annoying enough to bring the car in for service in December.


Since Christmas the car has been back to the dealer 4 times and for a total of 21 days. They have replaced the key batteries, the keys themselves, the KG computer module. The last time the dealer had the car was for 8 days - it was returned to me today with the dealer saying they tried everything they could think of but they could not reproduce the problem. Within 1/2 hour of the car's return I was locked out of it yet again!

So 2 scenarios -

1. if I leave the car unlocked and get in and press the start button it will work sometimes and sometimes it will say KEY NOT DETECTED. Even if I am waving the key in front of the speedometer. Once I press any button on the smart key itself, the car will now recognise the key and I can start the car.

2. If the car is locked, sometimes it will recognize the key and allow me to unlock the car and sometimes I will walk up with my key in my pocket and I am unable to open any door or the trunk and the speedometer will say KEY NOT DETECTED. Once I press any button on the smart key itself, the car will now recognise the key and I can enter and start the car.

Problem happens with both keys, in multiple locations (garage, driveway, office parking lot, local store) - doesn't seem to car what I have in my pocket or on my person - iPhone5, home security system key RFID key fob (works or fails with it or without it). I don't have a metal plate or screws anywhere in my body (that I know of).

Today when the car was dropped off, I tested the door action and all was fine. Then I drove it around to the back of my office building and locked it. I went upstairs and came back down 1/2 hour later to go out and pick up some lunch. LOCKED OUT. All 4 doors. Took key off key ring with security FOB and gave it to my friend who walked 50 feet away. Still locked out. Pressed unlock button on key - doors unlock. Then I drove 1 mile to a store, parked and locked the car and went inside. Came out 10 minutes later and same thing - LOCKED OUT. Gave my friend my cell phone and he took it 50 feet away - no joy. Pressed the button and drove back to work. One hour later back downstairs - everything exactly the same - same key, same jacket, same pocket and walk up to car and Voila! KG works.

I have video'ed this happening 3 times and sent to the dealer. It's probably happened a total of 30+ times. Dealer was able to have car fail initially but now won't fail for him.

Any ideas?