The SRS control unit sends a voltage signal to the seat belt buckles, since there are different resistance values buckled vs unbuckled a return voltage for one or the other value is *expected* in return. If the ECU sees a different voltage than expected the light stays on for 60-90 seconds. All it takes to damage a buckle is a drop of coffee or other substance. Sometimes the resistor just goes bad!
ON the 1984 thru 1987 the light(test time) is supposed to stay on for 10 seconds. 1988 & later the test period is only 4 seconds.
MERCEDES Benz Master Guild Technician (6 TIMES)
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44 years foreign automotive repair
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)