W210 - SRS Warning Light Coming On

[skemball]

Just got in the car this morning (no passenger) and the SRS light stays on when driving. Its never done this before with just me in the car but its has a long standing problem that when a front passenger is in the car the SRS light will occasionally/randomly come on and then go off but I very rarely have any passengers so have ignored this for the past few years.

I cant find much info' on the forum about this but do recall that there will be sensors in the seat bases to detect if the seat is in use?

Does anyone have any quick & easy checks that I can make? I'm handy with a spanner and multi-meter.

Thanks in advance

 

[d w124]

Airbag sensor

 

[Dieselman]

Seat occupancy sensor. There are two parts to this, one is the membrane switches for occupancy and the other is the child seat recognition which trips a reed switch.

You can test with a meter and pressing on the seat. The child seat switch has a diode in series so be aware.

I can't remember the pin outs, but had to change mine from a 2 to 3 pin when swapping the pad.

It's worth checking the integrity of the connection also as they can give trouble.

 

[skemball]

Thanks Dieselman for the tips.

I'm guessing that child seats have some metal strips on the base so that the reed switch detects when one is placed on the seat?

If so i could simulate that to check that part of the circuit. Had a look under the seat and there are 3 connectors fitted. Again I'm guessing 1 is for the seat belt buckle, 2 is for the child seat and 3 is for the seat occupancy.

 

[Dieselman]

The yellow connector is both parts of the occupancy sensor on different pins.