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2000 C230 Kompressor Sedan
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Discussion Starter · #1 · (Edited)
RESOLVED: 2000 C230 (W202) Unable to reset SRS light

Howdy all,

I have a newly purchased 2000 C230 and the SRS light was on at the time I purchased the car. The previous owner had the issue diagnosed by the dealership and a single fault code was found for the common problem with the child occupancy sensor in the front passenger seat.

After I purchased the car I took it to my local M-B independent technician who's been working on these cars for over 40 years and he confirmed the diagnosis.

I purchased the occupancy seat sensor from the local M-B dealer and installed it myself. I'm very mechanically inclined and have done lots of work on my cars over the years - so I was comfortable with doing this. As is often suggested, I disconnected the negative cable from the battery before performing the repair. Unfortunately, I had to reconnect the cable and drive the car without the passenger seat for a few days as i couldn't finish the job in one day.

I completed the repair a few days ago and yesterday returned to my mechanic to have him clear the code. Unfortunately, he was not able to do so. When he attached his scanner he now finds additional fault codes (probably from my driving the car without the passenger seat connected to the system).

Now here's the part that's got me (and my mechanic) stumped: When the scanner attempts to clear the codes, it comes back with an error message that says "Unable to communicate with ECU". Why would the scanner be able to communicate with the ECU to read the fault codes, and then later say that it is unable to communicate with the ECU when attempting to clear those codes?!?

I can't complete the state mandated "safety inspection until I get this issue resolved - so I am under some pressure as I had only 10 days from the time of registration to complete the safety inspection - and I'm already beyond that deadline.

Needless to say - any advice or guidance would be GREATLY appreciated.

Thanks in advance.
 

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1995 C220
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Not sure if this is gonna help, but first, try disconnecting negative cable for at least 30 minutes and see if codes still remain. If so, double check that your airbag fuse is good.

Not sure what your tech uses for a scan tool. My airbag light was on on my car, and our Mac Mentor scan tool couldnt shut it off. When we purchased a Snap on Modis in trade, for some reason it was able to read and shut off the airbag light with no problem. I cannot explain why this is, but it may be worth it to try another tool, unless he is using the factory tool.
 

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Discussion Starter · #3 ·
This SRS light issue has been the bane of my existence for the past 7 weeks and I FINALLY got it resolved today.

I successfully changed the child occupancy sensor in the front passenger seat myself and subsequently my mechanic (a Mercedes specialist) couldn't seem to find out why he was unable to reset the system. Even worse, there were actually MORE fault codes after I changed the sensor - leading me to conclude that all I achieved by doing the job myself was that I made yet another expensive tuition payment towards my ongoing mechanical education (will I ever graduate? Probalby not...) Bottom line: I was certain that, in spite of being careful, I still managed to screw things up.

And to add a little more intrigue to the story... more perplexing was the fact that my mechanic could read all the fault codes yet whenever he attempted to clear them he'd get an error message on his scanner that said "Unable to communicate with control module. So there was communication with the module to read the codes yet no communication to clear them. Right. This left both my mechanic and I scratching our collective heads (and simultaneously muttering "oh sh*t").

I left the car with him for two days and finally he was able to clear the codes. He wound up consulting with the company in the U.K. that markets his scanner and the software it runs. They required him to send them some sort of log and which ultimately generated a response that prescribed some sort of reprogramming of the srs module - which reset it.

So the airbag (SRS) light has finally gone out which meant that I was FINALLY able to bring my car for it's long-overdue annual state safety inspection (In the state of NY, it's an automatic failure of the test if the inspection station's scanner reveals any srs fault codes - so I couldn't even "fudge it" by taking out the bulb).

So, to recap - several weeks, lots of sweat and anguish and $420 dollars later - my car's SRS system is finally fixed and, once again, all is right with the world (....for now). And in my opinion, $420 all-in is not bad at all - as far as SRS repairs go anyway (it could have been a LOT worse, no doubt).

I'm especially grateful to my mechanic Horty (Foreign Car Motors, Norwalk CT) - A German gentleman who specializes in German cars (how's that for authenticity). A terrific guy who never gave up and who invested far more time in the repair than he charged me for.

And my thanks to all of you who took the time to responded to my post.

Happy Benzing...

Mark
 

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Discussion Starter · #4 ·
Not sure if this is gonna help, but first, try disconnecting negative cable for at least 30 minutes and see if codes still remain. If so, double check that your airbag fuse is good.

Not sure what your tech uses for a scan tool. My airbag light was on on my car, and our Mac Mentor scan tool couldnt shut it off. When we purchased a Snap on Modis in trade, for some reason it was able to read and shut off the airbag light with no problem. I cannot explain why this is, but it may be worth it to try another tool, unless he is using the factory tool.

Hey George - thanks for the good advice. I agree with your line of thinking. After reading many (way too many) forum entries and other pieces of information on the web, it seems that the SRS systems on these cars are very intricate (and temperamental). Many claimed that the only sure way to clear the SRS light on a Benz requires use of the Star Diagnostic System (SDS) which, unfortunately, means a trip to the dealer (time to lose another limb).

Fortunately, my problem got resolved today. Scroll down to my most recent post in this thread - the resolution speaks to your point...it's was all about the scanner. So you were definitely heading in the right direction.

Thanks again,
Mark
 

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Working in the collision repair business helps. I don't think its just a benz thing, I've noticed over the years that even the domestic cars are getting way more intricate with the air bags and the control modules in particular. Years ago when they first started installing them, if you had an airbag deployment or a seat belt deployment, it was a matter of changing the sensors in the area of the wreck, changing out the bags/tensioners, maybe a clock spring, then replace the control module, and all was good. Expensive, but for the most part easy to fix. The airbag light would even tell you what part was causing it to kick on, and 9 times out of ten, when you replace the part, the light goes out.

Not anymore. I've seen as many as ten different perimeter sensor on a car, not counting the control module, which itself can be used as a sensor. Then you can have dash airbags, steering wheel airbag, side curtain airbags, seat airbags, knee bolster air bags, seat belt pretensioners on all the seats, occupant classification sensors, seat track sensor......there is a ton of stuff that the computers now adays have to moniter, and if a deployment is needed, it has to be done within only a few thousandths of a second. So given all this, the computers have gotten way more complex, and it is getting harder and harder to work on them with anything but a factory scan tool. It can be done, but it cost a lot of money to stay up to date on a quality scan tool, and even then I've found that we have had to run a few cars to the dealer when our scanner fails to solve the problem. And more often than not, solving the problem requires reprogramming the control module. Was hoping in your situation you wouldn't need that, but glad that you had a good mechanic that you can trust that knows how to get to a solution. That can be half the battle right there.
 

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BTW, if you changed the OCS, it probably needed to be calibrated. And I have run into cars where when you change it, it does in fact require reprogramming. Some cars have a control module just dedicated to the OCS, usually mounted under the seat. As soon as it sees something has been changed, it kicks off a fault code. It makes sense now that you had to reprogram. I don't do enough Mercedes to say for sure, but this makes the most sense now that you mentioned that.
 

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Discussion Starter · #7 ·
Working in the collision repair business helps. I don't think its just a benz thing, I've noticed over the years that even the domestic cars are getting way more intricate with the air bags and the control modules in particular. Years ago when they first started installing them, if you had an airbag deployment or a seat belt deployment, it was a matter of changing the sensors in the area of the wreck, changing out the bags/tensioners, maybe a clock spring, then replace the control module, and all was good. Expensive, but for the most part easy to fix. The airbag light would even tell you what part was causing it to kick on, and 9 times out of ten, when you replace the part, the light goes out.

Not anymore. I've seen as many as ten different perimeter sensor on a car, not counting the control module, which itself can be used as a sensor. Then you can have dash airbags, steering wheel airbag, side curtain airbags, seat airbags, knee bolster air bags, seat belt pretensioners on all the seats, occupant classification sensors, seat track sensor......there is a ton of stuff that the computers now adays have to moniter, and if a deployment is needed, it has to be done within only a few thousandths of a second. So given all this, the computers have gotten way more complex, and it is getting harder and harder to work on them with anything but a factory scan tool. It can be done, but it cost a lot of money to stay up to date on a quality scan tool, and even then I've found that we have had to run a few cars to the dealer when our scanner fails to solve the problem. And more often than not, solving the problem requires reprogramming the control module. Was hoping in your situation you wouldn't need that, but glad that you had a good mechanic that you can trust that knows how to get to a solution. That can be half the battle right there.
George,

You obviously know your stuff... And in retrospect, and with your input, it now all makes sense to me too. I was just unnerved by the whole experience because I had elected to replace the Occupancy Sensor myself, in an interest to save money which, I've found, can sometimes boomerang on me and wind up costing me more because I botched something up in the process of "trying to save money". But, fortunately, given my years of experience in taking things apart (anything & everything from cars to computers) has long since "graduated" me from the level "oh shit, I have parts left over". I've pretty much made just about every mistake one can make when attempting to disassemble and (hopefully) reassemble stuff. It's been quite an education and I now have a vast knowledge of how things are designed and manufactured. But there is always something new to learn an keeping this in mind I make it a practice to do thorough research BEFORE I attempt the repair - and to take my time and not rush it. But I have limits like anyone else - that's why I am very grateful to have a great mechanic. He works with me and allows me to do some of my own work - and steps in when I need him (as in this case).

Thanks for all the input. As I mentioned earlier, I feel fortunate with this repairs as $420 (total parts and labor) is not at all bad when it comes to SRS repairs - even though I had to expend lots of energy and time (and expletives) I still think I got away with a bargain.

And btw, the OCS for my car had it's own control unit attached to it, which sits in a small carved out nacelle in the seat cushion. So, as you aptly surmised, it's not at all surprising (in retrospect) to have to have the SRS control module reprogrammed.

Well - all's well that ends well.

Thanks again.

Mark
 

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Hello Mark,

Quick question - when your sensor went out, did you experience any trouble with your wipers/turn signal switch?

For me, the SRS light usually comes on within 30 seconds of starting the car and then the turn signals go haywire - flashing to the opposite side from where the switch is engaged - and the windshield wipers/misters do not work and cause a clicking sound coming from somewhere in the dash.

I believe that this problem first started when I had to slam on the brakes in traffic. At that time, there was somebody sitting in the passenger seat. Since this OCS sensor appears to be a common problem - I'm fishing to see if you experienced any of these other problems as well. Unfortunately - similar to what George pointed out above - my Mac Mentor scanner doesn't find any codes.
 

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I like George have spent much of my adult life dealing with crash damaged vehicles, mainly 4wd and commercial. Not so much on the side or repair and certification (although I have done quite a bit of this with late model European cars) but on the side of parts supply and parts removal. I over my time have seen the subsystems and associated sub-subsystems double if not triple in the complexity and mass.

I can honestly see a future where not only does a vehicle require factory equipment to reprogram but where we will require actual robotic assistants to carry out the parts locating, fitting and calibration. It scares me a little and perhaps this time is still a way off but every year and model succession carries with it a more diverse, complex and utterly difficult set of equipments.

Also with the life-cycle 2 W202 cars it is quite common to have to recalibrate the SRS module with any replacement of the SRS/airbag componentry. I imagine they updated the firmware on his scanner to allow him to carry out the task.

Glad you have a solution and carried out the task properly, it is all to common to see in place those cheap, chinese OCS emulating plugins these days.
 
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