SRS warning light ON - Mercedes-Benz Forum
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post #1 of 21 (permalink) Old 09-20-2018, 10:46 PM Thread Starter
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SRS warning light ON

This has been bugging me for some time, SRS light is ON and the fault code is Child seat recognition. Can't get rid of it. What is this?

Why would 2-seater even have child seat recognition? How can I get rid of this "feature"? Can the control module be re-programed with DAS to ignore this?
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post #2 of 21 (permalink) Old 09-21-2018, 02:49 AM
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There is a sensor mat built into the passenger seat bottom that detects whether the seat is occupied or not - in order to prevent firing the airbag in case of a "light" child on the seat.
I guess you can override it mechanically but you'd certainly lose your safety certificate for the car if authorities find out, also in case of an accident it is quite a bad idea because you don't get the airbag for the passenger so would not suggest to do it. You can first check the connections to the mat, perhaps it is a simple plug that is broken or open, otherwise you'd need to replace that mat, it should be available with Mercedes - depending on the model year it might be one piece with the seat heater etc so can be a little complicated, I'd guess the max cost will be approx 600$ with Mercedes.

Furthermore there is an electronic sensor in the seat that connects with an electronic sender that is in the base of an original MB children seat. This will switch the airbag off as well, even if the weight of the children seat (and the kid as well) might be higher than the threshold for the upper sensor. Anyways the effect will be that your passenger does not have an airbag.
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post #3 of 21 (permalink) Old 09-21-2018, 07:05 AM
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Originally Posted by Photodude View Post
How can I get rid of this "feature"? Can the control module be re-programed with DAS to ignore this?
In 12 years of owning a 2003 SL one of the very few problems I have had is with the same B48 fault described here. Since the sensor works in conjunction with a baby seat I do not possess, spending $400 on a replacement sensor seemed silly. I used Star Diagnosis (specifically, DAS Developer Mode) to remove the sensor from the SRS system's coding, and the fault disappeared. It's not possible to do that on an R129.

If my R129 had this problem, I would remove the instrument cluster bulb which illuminates the SRS fault indicator.
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post #4 of 21 (permalink) Old 09-21-2018, 07:23 AM
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..If my R129 had this problem, I would remove the instrument cluster bulb which illuminates the SRS fault indicator.
I would agree with Bob on this one. And if your local regulations require inspection, where SRS light has to come one for few seconds with ignition on, then disappear, on my little brother's car, I've used this simple adjustable timer https://www.ebay.com/itm/12V-5A-Dela...r=581656520858 wired to an independent bulb attached to the factory SRS bulb location in the cluster, so it looks like "it works" as intended, passes inspections and does not annoy by staying on all the time.

There are always options of replacing the sensor $$$

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D
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post #5 of 21 (permalink) Old 09-21-2018, 09:34 AM Thread Starter
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In 12 years of owning a 2003 SL one of the very few problems I have had is with the same B48 fault described here. Since the sensor works in conjunction with a baby seat I do not possess, spending $400 on a replacement sensor seemed silly. I used Star Diagnosis (specifically, DAS Developer Mode) to remove the sensor from the SRS system's coding, and the fault disappeared. It's not possible to do that on an R129.

If my R129 had this problem, I would remove the instrument cluster bulb which illuminates the SRS fault indicator.
There is a "special functions" option in control unit programing. I requires full 17-digit vin # and some validation code after that, I'm curious what could be done there. Has anybody tried that?

But OK, as it is now, with child seat recognition fault code present… is passenger Air Bag disabled no matter who is in that seat? And if I remove interment cluster bulb, that air bag will still remain disabled right?
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post #6 of 21 (permalink) Old 09-21-2018, 10:36 AM
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Yes it will remain disabled - very dangerous for your passenger and a potential crime if an accident happens or if you ever sell it with this manipulation - not advised
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post #7 of 21 (permalink) Old 09-21-2018, 11:21 AM
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...with child seat recognition fault code present… is passenger Air Bag disabled no matter who is in that seat?
Intuitively, if the SRS controller were going to disable the passenger air bag, then it would illuminate the air bag "off" LED. If the LED is off, then I would expect the air bag to be fully operational.

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...a potential crime if an accident happens or if you ever sell it with this manipulation...
I believe the notion that someone in the U.S. would have legal exposure to removing an instrument cluster warning lamp is silly. A driver using a Mercedes "Baby Seat" has two indications that something is wrong prior to starting the engine: (1) the SRS lamp does not illuminate when the key is turned to position I, and (2) the air bag "off" LED is off. Nevertheless, if I had legal concerns then a simple alternative to removing the bulb is to install a non-working bulb.
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post #8 of 21 (permalink) Old 09-21-2018, 11:37 AM Thread Starter
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Yes it will remain disabled - very dangerous for your passenger and a potential crime if an accident happens or if you ever sell it with this manipulation - not advised
It is no more dangerous than driving a car without passenger air bag, which I still do occasionally and don't lose any sleep over that. It is annoying more than anything. It is silly design if true that I can't disable useless (for me) child sensor. If I'm not mistaken it is illegal to have child seat on the front seat anyway.
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post #9 of 21 (permalink) Old 09-21-2018, 11:42 AM Thread Starter
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Intuitively, if the SRS controller were going to disable the passenger air bag, then it would illuminate the air bag "off" LED. If the LED is off, then I would expect the air bag to be fully operational.
That's part of the problem here, the Air Bag off LED is still On with adult passenger in.
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post #10 of 21 (permalink) Old 09-21-2018, 12:08 PM
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...the Air Bag off LED is still On with adult passenger in.
Presuming the faulty B48 sensor is causing this, my personal choice would be to replace the sensor.
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