ML giving the following trouble code :

"P2203 Component Y3/6N3 speed sensor 3 is faulty"

I can't find this trouble code (P2203) or this component (Y3/6N3) anywhere.
Prior to throwing out this code the vehicle appears to be stuck in 3rd or 4th gear and moving from standing start seems like clutch slipping. Dash display indicates 'D' and tapping shifter to the left has no effect.
Turn key off and wait 10 seconds and then restart will reset the transmission and it runs back to normal.
Would appreciate any input.

2002 ML270 94k km's

regards