I have a c class w204.
recently I encountered weird some error messages on the dash AND THE AIBAG red light stays on.
So I got the Icarsoft i980 and I scanned it .
it showed 2 major errors :
1- power supply is too high ( I can erase it from the scanner but keeps coming back after a while)
2- there is internal fault in control unit “airbag” ( I cannot erase this error from scanner )
i went to bosh service center and they put it on their own scanner and they told me I have problem with voltage regulator that needs to be fixed after that we will check if airbag RED LIGHT egoes off or we need to change the airbag control unit located next to gear stick between seats
I was so confused by their diagnostic so I went to another service center and they put the car on scanner and they told me to ignore the voltage thing and replace the SRS airbag control unit only.
I have read in some forums that high voltage could cause the car to turn off the SRS control unit to protect it and once the high voltage issue is sorted then the SRS will be back to normal.