Our GLK350 4Matic died making a grinding noise. I had thought the transmission or transfer case was shot, and had it towed home to see what I could do to repair it. The only code was the transmission 721, output speed sensor implausible reading, (indicating the speed of the output shaft sensor, and the four wheel speed sensors did not match. There were no wheel speed sensor codes from the ESP controller, so the error would gave to be in the transmission output speed sensor

Figuring our I would have to replace the valve-body/connector-plate+ecu or the whole transmission (in case the transfer case was shot) or something else, I began to debug the problem.

I jacked up the car off the ground trying to determine if it was the transfer case mechanical breakdown, and discovered one wheel, was spinning freely (the drivers side front wheel) , when in park and all other wheels locked.

I traced the issue to a chewed up spline, in the joint where the short front left drivers side CV half shaft connects on to the center shaft that runs through the engine oil pan. I can see this might require replacement of both the center engine oil pan shaft (where the splines are chewed up) and the left front CV shaft.

Has anyone else seen this issue, and solved it? all comments are welcome, thanks.

At this point, with just over 180,000 miles on this 2011 car, I might even consider jamming on the shaft with JB-weld and then getting a mechanic with a spot welder to weld the two sections together.

Thanks,

Alan

here is a picture of the splines, it seems that a lot of corrosion also took place in this spot