Photo DIY - SRS Seat Sensor replacement
Your SRS light has come on and stays on, Also you noticed that the airbag off light stays on as well. Your car has never been in an accident, and your bags and belts have never deployed. You have some basic mechanical aptitude and don’t want to pay a dealer 500-800 $US for this repair. Read On…
It is not necessary but best to look for an independent mechanic shop that displays the 'pie', and have the codes read, this will tell you exactly what the problem is. Most will not charge for this service, and unless you have the MB software and can read the exact pin, you can’t do it..
Lets try and address the most common questions regarding this condition.
Q; - Is this a safety issue, the car still runs and a friend of mine who has a 2000 210 has a piece of electrical tape over the light and just drives it. Do the air bags still work?
A; No, Operation of all SRS devices are unpredictable, they may not fire at all, or they may fire for no reason
Q; How many Sensors are there and where are they?
A; Many.. The SRS system has a pre-tensioner in each seat belt, several air bags, sensors throughout the car to activate same, and a child sensor in the front passenger seat.
Q; Before I tear my car apart I would like to know as much as I can, what the module looks like and yhe functionality and design information
A; The child sensor adjusts air bag and seat belt level for the front passenger, and effects the functionality of several other devices.
Q; Is a sensor of some kind in the drivers seat?
A: No, a seat belt switch, and seat belt tensioner , and air bags.
Q; If I replace the Ass Mass will the light go off?
A; BE Clear Here, when you fix the fault, The Light WILL go off by itself if all faults have been corrected.
Q; How do I do this repair myself?
A; On the next posts, you will see a series of pics, but the procedure is,,,
1. At some point, have the codes read, by an inde, (PIC 1 ) as having the seat pad SRS light on will 'MASK' other ( emergency tensioning retractor belt and bag) faults.
2. Buy a NEW sensor first, (PIC 2 ) I have not seen ANY signs of wear ( wires, scraping, breaks ) at all. The sensor 'dots' fail with use/age. Sensors cost 140 US$ at MB.
3. TIP- Take the seat out of the car, period. If you have never done one, and are not an MB tech, or leather repair expert, 5 bolts and some clips and the seat is out. Don't even try to in car cover remove. you will me$$ it up!
4. TIP- Allow an extra 2 hours to shampoo the carpet under BOTH front seats. which is what you will do when you see all the gack under the seat. My car gets 'mini detailed' weekly and it still had lots of filth under the seat(s). Record amount of coins found so far.. $16.83 US$’
5. Unplug all wires from the connector block (PIC 6-7 )
6. Snap off the bolt covers (PIC 8 )
7. Remove all four 'Torx' type bolts (PIC 9-10 )that secure seat rails in place on the car floor.
8. Pull OUT not up on seat belt bolt cover(PIC 11 ) and remove bolt.
9. Release the wire cable (PIC 12 )
10. Tip the seat top down and remove the complete car seat from the car.
11. Remove the connector block and unplug the yellow sensor (PIC 13 ) connector from it's housing under the seat.
12.Take off the plastic side covers.
13. Loosen the 2 back bolts, (PIC 14-15 ) and remove the 2 front ones, This is optional and done to make the job easier.
14. Push down on the leather, (PIC 16-17 ) and pull out the bar that holds it to the frame.
15. Twist 90 degrees on the plastic ‘butterfly’ clips, (PIC 18-19-20 ) and release the leather cover.
16. Change out the sensor pad (PIC 21-22-23 ).
17. Once you have removed the sensor pad unit replacement is simply a reverse procedure. (PIC 24-25-26 )
It is not necessary but best to look for an independent mechanic shop that displays the 'pie', and have the codes read, this will tell you exactly what the problem is. Most will not charge for this service, and unless you have the MB software and can read the exact pin, you can’t do it..
Lets try and address the most common questions regarding this condition.
Q; - Is this a safety issue, the car still runs and a friend of mine who has a 2000 210 has a piece of electrical tape over the light and just drives it. Do the air bags still work?
A; No, Operation of all SRS devices are unpredictable, they may not fire at all, or they may fire for no reason
Q; How many Sensors are there and where are they?
A; Many.. The SRS system has a pre-tensioner in each seat belt, several air bags, sensors throughout the car to activate same, and a child sensor in the front passenger seat.
Q; Before I tear my car apart I would like to know as much as I can, what the module looks like and yhe functionality and design information
A; The child sensor adjusts air bag and seat belt level for the front passenger, and effects the functionality of several other devices.
Q; Is a sensor of some kind in the drivers seat?
A: No, a seat belt switch, and seat belt tensioner , and air bags.
Q; If I replace the Ass Mass will the light go off?
A; BE Clear Here, when you fix the fault, The Light WILL go off by itself if all faults have been corrected.
Q; How do I do this repair myself?
A; On the next posts, you will see a series of pics, but the procedure is,,,
1. At some point, have the codes read, by an inde, (PIC 1 ) as having the seat pad SRS light on will 'MASK' other ( emergency tensioning retractor belt and bag) faults.
2. Buy a NEW sensor first, (PIC 2 ) I have not seen ANY signs of wear ( wires, scraping, breaks ) at all. The sensor 'dots' fail with use/age. Sensors cost 140 US$ at MB.
3. TIP- Take the seat out of the car, period. If you have never done one, and are not an MB tech, or leather repair expert, 5 bolts and some clips and the seat is out. Don't even try to in car cover remove. you will me$$ it up!
4. TIP- Allow an extra 2 hours to shampoo the carpet under BOTH front seats. which is what you will do when you see all the gack under the seat. My car gets 'mini detailed' weekly and it still had lots of filth under the seat(s). Record amount of coins found so far.. $16.83 US$’
5. Unplug all wires from the connector block (PIC 6-7 )
6. Snap off the bolt covers (PIC 8 )
7. Remove all four 'Torx' type bolts (PIC 9-10 )that secure seat rails in place on the car floor.
8. Pull OUT not up on seat belt bolt cover(PIC 11 ) and remove bolt.
9. Release the wire cable (PIC 12 )
10. Tip the seat top down and remove the complete car seat from the car.
11. Remove the connector block and unplug the yellow sensor (PIC 13 ) connector from it's housing under the seat.
12.Take off the plastic side covers.
13. Loosen the 2 back bolts, (PIC 14-15 ) and remove the 2 front ones, This is optional and done to make the job easier.
14. Push down on the leather, (PIC 16-17 ) and pull out the bar that holds it to the frame.
15. Twist 90 degrees on the plastic ‘butterfly’ clips, (PIC 18-19-20 ) and release the leather cover.
16. Change out the sensor pad (PIC 21-22-23 ).
17. Once you have removed the sensor pad unit replacement is simply a reverse procedure. (PIC 24-25-26 )
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141 - 158 of 158 Posts
Anyone in the los angeles or orange county area familiar with the procedure willing to help with this fix for a fee? I barely was able to help my son put together his lego set 
and have been putting off this repair.
and have been putting off this repair.Great post with many views. Nothing for 12 months so everybody must have fixed their passenger sensors
I now have the srs light on, was intermittent but then hard on.
suspected it was the passenger sensor,but before hacking into wire I got the codes read. Indy had a snap-on reader.
result: Airbag 9025 : component B48(front passenger seat occupied and child seat recognition) faulty.
Car is A209 clk cabriolet, 2008 build, and a few differences to the photos. Australian car.
Has heated and pneumatic multi-form seats. All the complications!
Was Hoping to be lucky and only have to fix broken wire.
Checked continuity of red,brown,white wires up to where they disappeared into seat using ohm on multimeter. All ok.
Dismantled seat enough to get the box for the pressure pad exposed, with the intention of flipping its lid and doing full end to end continuity. HA!, foiled again! Box seems to be filled completely with hard plastic, so can’t get to the internal end of the wires.
While re-testing continuity, I noticed that there was some connectivity between the pins on the plug itself. Some resistance but NOT open circuit.
QUESTION: does this mean that the wires are all actually intact and not the problem as they allow current flow to the pad and back?
for those with a bit more electrical nouse than I, does it seem ok that the circuit is closed (with resistance) when the pad has no weight on it? Ie what is normal for a working pad?
If this is the type that transmits pulses (ie not variable resistance type) what should be seen?
ALSO: the control levers for the seat pneumatics are attached to the side of the seat with POP RIVETS. And.... the rivets go thru the seat cover making it impossible to remove. Is this normal? See two pop rivets in photo.
![Personal protective equipment Auto part Seat belt Wetsuit Vehicle]()
Help appreciated.
I now have the srs light on, was intermittent but then hard on.
suspected it was the passenger sensor,but before hacking into wire I got the codes read. Indy had a snap-on reader.
result: Airbag 9025 : component B48(front passenger seat occupied and child seat recognition) faulty.
Car is A209 clk cabriolet, 2008 build, and a few differences to the photos. Australian car.
Has heated and pneumatic multi-form seats. All the complications!
Was Hoping to be lucky and only have to fix broken wire.
Checked continuity of red,brown,white wires up to where they disappeared into seat using ohm on multimeter. All ok.
Dismantled seat enough to get the box for the pressure pad exposed, with the intention of flipping its lid and doing full end to end continuity. HA!, foiled again! Box seems to be filled completely with hard plastic, so can’t get to the internal end of the wires.
While re-testing continuity, I noticed that there was some connectivity between the pins on the plug itself. Some resistance but NOT open circuit.
QUESTION: does this mean that the wires are all actually intact and not the problem as they allow current flow to the pad and back?
for those with a bit more electrical nouse than I, does it seem ok that the circuit is closed (with resistance) when the pad has no weight on it? Ie what is normal for a working pad?
If this is the type that transmits pulses (ie not variable resistance type) what should be seen?
ALSO: the control levers for the seat pneumatics are attached to the side of the seat with POP RIVETS. And.... the rivets go thru the seat cover making it impossible to remove. Is this normal? See two pop rivets in photo.
Help appreciated.
141 - 158 of 158 Posts
