Long story about repairs to my 2006 MCS R53 so stick with me.
I've had an Airbag light for several years. Reading the OBD codes showed a bad passenger seat occupancy sensor. Bought a new bottom cushion and installed it. No change in the light or code. Clear the code and it comes back immediately. Tried to ignore it but after a while that didn't work. Stripped out the front seats and carpet. Checked all the wiring for chaffing or opens as best as you can without cutting open the bundles. Didn't find any problems there. Turned to shotgunning parts, dealer gave me a new part number and a $1700.00 price, which I declined. Online I found a used/tested version of the new part number for 30 bucks. Took a chance and bought it. Once installed OBD shows no communication. Took the car to an independent shop and asked them to program the controller. After an hour they returned the car and said they were not successful. A few weeks later I found a used/tested version of the original part number and bought it. Now i have 3 MRS controllers.
Several weeks pass, the car is still parked and gutted so I decided to tackle this myself. Bought a new ICOM Next, bought a new laptop, and subscribed to ISTA+. After several days I managed to get ISTA and ISTA/P install and configured. With the original controller in place ISTA reports a defective passenger occupancy sensor (same as my OBD reader). Installed the original part number controller, connected ISTA/P and followed the instructions. Unit encoded successfully but still reported faults, shows no communication to the K-buss. Used ISTA troubleshooting process and found no problems. The steps involved verifying power, ground and continuity to the back of the instrument cluster. Tried to program again, saw a successful report from ISTA/P again but still had a no K-buss communication.
Installed the updated part number unit, encoded with ISTA/P successfully. Once again had no K-buss communication. Stuck the original controller back in and read the faults, defective passenger seat sensor. Out of desperation I stuck the old seat sensor in which didn't change the faults. Left the old seat sensor in and changed to the new part number controller. Encoded the controller successfully but still shows K-buss errors. I believe the original controller is falsely showing a seat sensor error. I support that based on swapping to a new sensor without changing the fault. Both used controllers show a K-buss error, I think it's unlikely two used controllers with different part numbers, purchased from different vendors at different times both claiming to have been tested and verified would have the same failure.
Now I'm stuck! Any suggestions? I don't mind spending money on the car but I'm not spending 1700 bucks for a new controller that I don't think will solve the problem.

 

The new modules need to be coded, not programmed. You'll need to use NCSExpert which should have came as part of the ISTA package.

But, I don't think you have a problem with the module (old or new). The connectors under the seats are notorious for causing airbag related fault codes - Even though they look fine they can have a high enough ohm reading to cause problems.