Mercedes has extended the planned replacement of all airbags. There are none that are yet up for replacement. The planned replacement was a liability issue. Since long term effects of humidity and heat couldn't be planned there was an original planned service life. When the first bags started hitting this interval in 1995 they extended the life as a history was known by this time.
Diagnostic fault codes can be read and erased using the instructions given in the DIY section under evaluating electronic engine controls (the method for doing impulse codes are the same for all systems - the pin to read is #6). There are 10 different fault code possibilities for the 91 126 chassis.
#1 no malfunction
#2 SRS control unit
#3 Driver airbag
#4 Front passenger airbag
#5 Driver seat belt buckle
#6 Front passenger seat belt buckle
#7 Front passenger airbag resistor
#8 Voltage supply
#9 Warning lamp defective
#10 SRS control unit was activated - was in a accident
#10 is never erasable!
Bosch Master, ASE Master, L1
33 years MB technician