I had something strange happen. My car had been displaying an SRS error message on start up that went away as soon as I drove about a quarter mile. I searched on this forum and Benzworld and some posters suggested that my battery was weak. Since the battery was six years old and was reading low (11.9-12,0 volts), I replaced the battery on a Saturday (April 14th) with a Bosch Platinum AGM battery (49-850BAGM) which I bought at PepBoys.

After the install, the voltage reading at rest increased to 12.7 (from the 11.9 to 12.0 range.) The SRS message was not on. I ran some errands later that day and confirmed the operation.

Because the weather was nice and I didn't need to transport passengers I drove my sports car for a week. Then, on Sunday (April 22nd) the car wouldn't start. I checked the battery with a volt meter and it read 4 volts. I took the battery back to Pep Boys on Monday evening. It was too late for them to test the battery on Monday night, but they called me today and said that it wouldn't charge up. They exchanged it this evening (Tuesday) without any snags.

Although the battery was getting weak before I bought the new one, I hadn't had any problem with it going completely flat. So, I guess it is possible that the first battery I bought was defective. However, I'm concerned that something in the car caused the battery to drain.

Anyone have suggestions for what I might need to check?

 

Many of the electronics in the W203 are CR*P! Consider that they make the mega POS GM cars look good.

Check the voltage when the car is idling. It should be 13.5-14.5v.
If not, the alternator or voltage regulator is bad. Seems like the voltage regulators go on these cars.

The seat controller is known to go bad and cause a battery draw even when the car is off. You can check by measuring the current of the system when the car is off.
Or, with the car off, measure the battery voltage. Disconnect the seat controller or yank the fuse. See if the battery voltage increased by more than 0.1v. If it did, the seat controller is likely bad.


Good Luck!

 

 

I put the new battery in this morning. I left the car for a couple of minutes after completing the installation. When I came back, the tail lights were on. I disconnected the negative terminal to keep from draining the battery. I brought a socket wrench with me when I ran some errands. I noticed at one of my stops that one of the parking lights appeared to be on. (It was very sunny today, so it was hard to tell.) Is this indicative of a faulty light switch or is there a control module somewhere that could be defective?

I had a minor fender bender about a month ago and the other guy's insurance company paid to have the front end patched up. (Photo attached.) Could that have damaged a lighting component?

I've been searching on terms like "light switch" and I haven't seen anyone else experiencing this problem. Any suggestions that will point me in the right direction will be appreciated.

 

Someone on another forum suggested that I may have a damaged SAM. Does anyone know whether the iCarsoft MB-II can diagnose SAM errors: http://www.icarsoft.com/web/icarsoft...48eyzy9_1.html

It may be worth investing in the diagnostic tool before I spend a lot of money throwing parts at the car or taking it to the dealer.

 

Did you jump start the car at all? Light switches do not fail on w203, odd lights that remain on , for sure the SAM is faulty. Sometimes scanning for codes will show no lighting faults. But if lights stay on there can be only one culprit, the SAM!

 

 

Rear lights = rear Sam
Front lights = front Sam.
That MBii scanner looks pretty good for the price! Hopefully it can scan all the body systems, like the Sam's, maybe someone who's has the tool can tell us

 

It shouild scan the SAM.
I'm dealing with emissions issues, and OBD is giving me a
P0420 pending fault, but ICarsoft says UNKNOWN CODE.
Seriously? Looking up the Mercedes specific code spewed by ICarsoft on the net, immediately
translated to the P0420. I might need a new cat, but trying a spacer on the lower 02 sensor 1st, been
known to work, a trick.

I'm not looking for help here,. just perspective on iCarsoft.
And this was with the latest updates.
All in all though, at least it reads the Mercedes codes, even if it doesn't always know what they are.

 

At about the 2 minute 30 second mark of this video: you can see a menu selection for a front and rear SAM for an E Class. I think it's safe to assume that it should have them for a C Class.
I made an offer for an open box unit. For about the cost of an hour of labor at an independent shop in my area I think it is a sensible purchase.

 

I received my iCarsoft MBII system and read the codes in the various systems. Here's what I found:

Front SAM:
B1035
Switch S1s1 (Exterior light switch supplies an implausible value)
I noted the following symptoms:
The green light indicating that the headlights were on illuminates on the dash and the lights themselves come on even when the switch is off. I tried turning the lights on and off and that had no effect on the lights. They would turn off on their own from time to time, but when I competed my ride to work, the lights remained on. I had to disconnect the battery while I was working. Also, the light illuminating the switch itself remained on even when the other dash lights were off.

My suspicion is that the light switch is defective and the solution is to replace it. New switches are pricey, so I may buy a used one.

Air bag
9002
Control module N2/7 (Restraint systems control unit) (Circuit 15R) No voltage when voltage present at circuit 15
9007C
Fault in CAN communication control unit WSS
9007D
Fault in CAN communication control unit WSS
907E
Fault in CAN communication control unit WSS
9083
A component of control unit WSS may be defective

The SRS warning light comes on occasionally, with instructions to drive to the workshop. The light and warning shut off after about a mile of driving. It has stayed off for up to about 3 days before reappearing.

I have been searching forums and the Internet in general without finding anyone with similar issues. If anyone has suggestions or experience, please share.

Thanks

 

I followed a suggestion on Benzworld and checked all the air bag related fuses (2 in the front SAM and 2 in the side of the dash) and re-seated them firmly. I cleared the air bag and front SAM modules of codes. I then removed the light switch and started the car. Removing the light switch connector must disable the instrument cluster because it was dead and there was an error message in the front SAM stating there was no communication with the cluster. The lights were on.

I reinstalled the light switch. When I restarted the car the light switch and the instrument cluster worked properly. The lights stayed off when the switch was in the off position. I scanned the SAM and the air bag modules a few times with the car off and with the car running and the codes have not returned.

I am heading out to run some errands. I will keep a wrench with me in case I have to disconnect the battery.

Maybe something was loose, but I am not convinced that I have fixed the issue.

 

I visited my Mom today - a 200 mile round trip. When I returned, I scanned the car. There were no codes in the Front Sam or the Air Bag module. When I read the actual values in the light switch it said that Switch S1s1 had a "fault status." I'm planning to replace the switch with a used one and then check the replacement for errors.

Please let me know whether you would do the same thing in my situation.

 

It seems like a used switch goes for ~$50 on ebay.
So, imho, it's a no brainer!

Fwiw, $50 for even a dumb(new) headlight switch is cheap!
I haven't see any other headlight switch threads in the past few years. So, it doesn't seem like a high/typical wear/time-related-failure item.


Imho, if someone wants a cheap car to own and fix, buy a Civic. Or, imho, maybe that person would be much better off being under conservatorship.



Good Luck!

 

Thanks for affirming my thought process. Like you, I didn't see any reports of light switch failures when I searched the forums. While it seems like a reliable part, I may own the exception to the rule. I'm the third or fourth owner of my car, so I'm not sure how it was treated by previous owners. I ordered a replacement on Ebay - $45 shipped. There were some less expensive ones available, but I paid about 5 dollars more to buy one in excellent cosmetic shape from a seller with 100% positive feedback.

When I replaced my fuel filler assembly with the updated version to fix my evap system leak I was about 95% sure I had focused on the correct problem. I'm feeling slightly less certain about the light switch issue, but I don't think I'm just throwing a part at the car. A defective light switch matches the evidence.

It's interesting that you mention the Civic. I bought a used 2006 Honda Civic (EX-5 speed manual transmission) for my daughter about 6 years ago. I have only had to perform regular maintenance on the car. The driving experience is just not on the same level as my C230, so I guess lower reliability is part of the price you pay. My wife and I were discussing Mercedes ownership on our drive today. I also own a 2000 Porsche Boxster and my wife said that it is "We know the situation is getting strange when we consider the Porsche the reliable car." I told her it was like being married to a beautiful and charming woman. They are going to be higher maintenance, but you only live once.

 

I've continued to plug away at this. The replacement switch did not solve the problem. I continued to scan the car focusing on the front SAM and the SRS module. The only time I would see the SRS codes would be when I let the car sit overnight. The warning would come on in the morning, but go off after driving about a half mile. The first code in the front SAM would always be 9002 - Control module N2/7 (Restraint systems control unit) (Circuit 15R) no voltage when voltage present at circuit 15.

I finally thought it through and decided to scan the all the modules again. There was a code in the rear SAM - B1078 - Fault in communication with component H3/1 (Alarm signal siren with additional battery) or there is a cable fault. (The first time I scanned the rear SAM it was loaded with codes about defective light bulbs, so I cleared it without looking too closely. This may have caused me to overlook the B1078 code.)

I did some research on B1078 and found that several people indicated it caused lights to operate at random and drain the battery. I first checked the wiring (the siren is in the passenger side front wheel well.) The wiring looked OK, so I took the plunge and ordered a new siren. It set me back $135. I installed in this morning, cleared the code from the rear SAM and did some typical Saturday errands.

Currently, I have no codes. In addition, when I lock the car I now hear three beeps from the siren. I hear one when I unlock the door. During my entire 10 months of ownership, I have not heard anything other than the sound of the locks when locking or unlocking the car.

My current working theory is that the siren has been defective the entire time I owned the car and it was the cause of the drain on the battery. My driving habits (mostly trips of 30 miles each way to work and a frequent 200 mile trek on the weekend) kept the battery well charged. Eventually the drain caught up with the battery and when the voltage got too low, it triggered the problem with the SRS system.

I'll keep an eye on it and see whether it stays fixed. The iCarsoft may have paid for itself if it found the cause of this problem.

 

Yes I have had this before, the siren can cause battery drain. But should not affect SRS at all!

 

Thanks for the reply.

I took a 200+ mile drive today and I did not see the SRS warning at any time. I am not certain that validates my theory that the drain on the battery caused a low-voltage situation that triggered the airbag warning. I'll keep checking the car and post an update in about a week.

 

Clearly this is going to take some persistence. Here's an update.

I took the car on a brief drive this morning. I drove about 5 miles to the gym and stayed there for about 90 minutes. Then I drove about a mile and stopped at a grocery store to buy a birthday cake for my wife. At this point, everything looked good. I drove the remaining distance home (about 4 miles) and because my wife was at work, I pulled into her garage and parked the car with the the windows down and the doors unlocked. I started on some yard work and when I entered the garage to look for some wasp and hornet killer (I'll spare you the details) the lights on the car were flashing and I couldn't get them to turn off.

When I opened the car door, the message "Turn off lights" was on the message screen. (The same message I see when I forget to turn off the headlights and turn the car off and open the door.) I scanned the front SAM and got the message: B1035 Switch S1s1 (Exterior light switch supplies an implausible value) When I read the actual values it stated that their was a fault in the switch. When I started the car to move it out of the garage, the SRS - drive to workshop message appeared.

It is unusual for me to leave the car unlocked for more than a few minutes, so I'm wondering whether something about leaving the car unlocked triggered the event with the lights. The first time the lights acted this way, the car was also sitting unlocked in the garage.

Although my observations and the iCarsoft data suggest the light switch is faulty, I have already replaced it. I did replace my original switch with a used part I bought on ebay, so it is possible that the replacement was defective. However, I think that is a low probability event because I haven't seen a lot of people posting about failed light switches. Before I buy a new light switch I want to rule out any other possibilities.

Any suggestion would be appreciated.

 

Can iCarsoft display the real-time data of the switch?
If so, I'd first start to see that the switch behaves in a reasonable manner.
Then, when you get the error again, check the status of the switch, and see how it's behaving (when turned off/on/etc).

I agree that it's unlikely the switch. From what I've read, and know about these era C-class/E-class cars, it may be more likely a bad connection at a CAN-bus junction point, or a bad cable.
Maybe someone did some work on the car once, and pushed/pulled/moved a CAN bus wire/connection?

Good luck!

 

Thanks for the suggestions.

The iCarsoft has a setting that reads actual values. I need to learn more about it before I judge whether it will be helpful. Right now I'm having trouble understanding what it is telling me. For example, when I scan the light module it has about 7 data points that it will read and display. The first one is the light switch and all it says is that there is a fault. When I turn the light switch on and off with the iCarsoft connected the reading doesn't change. I don't have some of the options controlled by the light switch module (e.g. folding mirrors) and the fact there is no data for them makes sense. But for some of the ones I do have like the mirror controls, it seems like the ICarsoft is not providing some readings I expect.. I'll take a video and post it to YouTube when I have some time so that I can show what the system is doing.

I did some research on the CAN bus issues and I haven't been able to find someone with the exact same issue. Most of the posts I saw involved the cars prior to 2005 and I think they may have slightly different components. What I have been able to glean from my CAN bus readings is that some posters think that something is keeping the car from "going to sleep" which causes a current draw and subsequent voltage drop. Once the voltage drops below a certain level, chaos (such as my flashing lights) ensues.

I know that I did not lock the car before yesterday's incident and that was also the case in at least one (if not all) of the previous incidents. So, it is possible that a component was staying "awake" and eventually caused a drain on the electrical system. Locking the car may cause the car to go into sleep mode and avoid the drain on the battery.

I'll keep working on this and post if I find a solution.

 

From a CAN-bus issues fault, it's not that relevant "if it's the same exact issue".

I love analogies. I used them all the time when I used to teach.

Consider CAN like electrical power extensions.
Let's say you have a flaky clock that is connected by 4 extension cords and some extension cords have multiple taps.
You may have a bad extension cord, or you may have an intermittent extension cord. Or, maybe the device at the end of the extension cord is bad or flaky.

So, how do you go about figuring out what the problem is above?
If you have a DVM (digital volt meter (good), or maybe a storage oscilloscope (much better!)), you can look at the voltage (or with a 'scope/can-bus-logger - the CAN bus traffic itself) at the connection points along the way.
Also, you can look at each connection to make sure that it's firm and stable.
Also, you can look at the end of each extension cord to see if it looks bad.
You can look at each extension cord to see if you see a break.
You can "wiggle test" each extension cord to see if it effects the readings. And so on.

Btw, it's similar when a person has a problem with their cable at a house. The tech will use a tool to see how good the signal is at various points. They'll also look at the connections and the cables, and maybe do a wiggle test.
Then again, if they are Comcast, they just tell the customer to go ********* themselves. I know a number of people that have had that response. I assume that it's different at different offices. And, maybe they've gotten better now.
Fwiw, 5G and small satellites may finally help to break the cable monopolies, But, don't hold your breath.
Btw, the 5G standard will be good for very dense city environments with a lot of big apartment buildings. Think NYC, Boston, etc. However, the distance and wall penetration of 5G (very high frequency) is not good at all.

Fwiw, yes, I'm an engineering geek.

 

Forget wasting your time checking the can bus at different points! You wasting your time. If there is CAN issues you can be sure its logged as a fault. You mention the SRS warning lamp, but what are the SRS fault codes? W203 lights switches hardly ever fail, and you have already tried another. So my next step would be the front SAM, remove it open it and check for water ingress. Leaving the car unlocked will not affect anything. The bus will still go to sleep. If your lights are flickering and you have a fault for light switch then check the inputs to the SAM on actual values.
The car never stood long enough from the time you parked it until the lights flickered to be a low voltage issue.
Good luck

 

If the front seats move before you start the engine, check this system. It is cause to drain your battery.

 

Thanks for the continued support. I've driven the car back and forth to work three times (30 miles each easy) since the "event" on Monday. The SRS/Drive to workshop message has not displayed on the dash board message screen. However, there were 5 codes in the SRS module:
9002 - Control module N2/7 (Restraint systems control unit) (Circuit 15R) No voltage when voltage present at circuit 15
907C - Fault in CAN communication with control unit WSS
907D- Fault in CAN communication with control unit WSS
907E - Fault in CAN communication with control unit WSS
9083 A component of control unit WSS may be defective for more information read out the DTC of control unit WSS

The actual values of the light switch still say "Fault Status"

I'm surprised that I'm not receiving an SRS error on the dash information screen with that number of codes in the SRS module.

So, I'm thinking of taking a look at the SRS module in the dash. I would appreciate any guidance on whether this is a logical next step and what I should be looking for.

Thanks,