Hi there,

My car has been giving me problems lately. It won't start until i get it jumped. I initially checked the battery cables and noticed one cable was a little loose, so i cleaned it, tightened it, and charged the battery. There were no problems for couple of weeks. Today, it was 38 degrees and the car wouldn't start !!!!! My battery is 2 years and 9month old. Is this a normal time to have it replaced?

I checked the sensor's (sensor # 24) and the battery voltage was 0.85v, which is pretty low I think.

I've read some posts regarding power seat modules draining the battery, but how would i know if these modules are the cause of the problem? The power seats work fine on my car (they don't act awkward and the memory function also works fine).

By the way, with the car off, how much current should the battery hold?

Thank you

 

batteries hold about 11-13v although they are rated as 12. The real key is the amount of amps that it puts out as you could have a bad battery that shows enough v but does not have enough amps to crank the car. Think of volts as horsepower and amps as torque.

When the thermometer drops, the output of the battery (namely amps) drops significantly. That is why on a cold day your battery will show 12v but it barely cranks.

Batteries can die in any amount time, I just replaced the battery on my TR6 on Friday and it was only a year old. All you need is 1 bad cell and the thing is toast.

Factors that affect life on the unit:
cold and a frozen battery is usually toast
overcharging
over heating of the battery
vibration
number of cycles from discharge to charge
bad alternator
bad voltage regulator
too much draw on the battery, powering lots of light and a kick *** sound system that will wake the dead

 

So i've read that the battery should not draw more than 100mA while at rest. If I want to measure the current on my battery, I would have to disconnect the positive (+ve) lead and attach a Multimeter in series. In previous posts it's recommeneded to diconnect the negative (-ve) lead first. Does it matter? If yes, then how do i measure the current draw?

 

Is it the Mercedes Benz battery that you are talking about. Had the same problem last year with mine in cold weather. Try turning the car on and undoing the cable(positive and negative) if the car turns off then its the alternator, if it stays running its the battery. I took my car to the dealership and they tried charging me $400 for the seat module and other things. Did the battery replacement from Autozone and cost me $110 with 5 year warranty. Have not had any problems since then.

 

if the power seats work, that doesn't mean there is nothing wrong with it. my driver side was working fine and passenger side did not work at all... but both were draining batteries... u need to take it to dealer to have it checked...

 

Maybe your battery needs maintenance? My 02 C230 has the original MB battery. This battery requires maintenance! Part of Service B is to top off the battery fluid levels. If you're not handy, take it in and have the dealer check it. If you are handy (read: car-savvy enough to not complain if you break something), you can try checking and maintaining the battery yourself.

Disconnect the battery first.

There are 6 large plastic philips-head screws on top of my battery. Each of these covers up one of the battery cells, and the fluid level in the cells needs to be maintained. You can fill up the cells with distilled (de-ionized) water, or buy a container of battery acid from your local car supply store. If the battery fluid level was low for a long time, you may need a new battery. But, the first time I checked mine (I bought it used), the fluid levels were very low (I added almost one quart of fluid overall), and my battery has been fine for the 3 years I have had the car.

 

Ditto-
Car mfg'd 12/2001-
Still on Original Battery.
Knew to top it off from reading the forums.
Was never done by the dealer.
Idiots.

(Nor did they every clean the contacts)

 

Hi folks,

Here's the latest updates. Lets see if you guys can help me out here.

I took the car to the dealer. It turned out the battery was replaced exactly 2 years ago and it was still under warranty. They checked the battery and it was OK (no dead cells what so ever). They tested the charging system and it was also OK. They did a current draw test and they found a 1.4 Amps draw which is a lot . They said the current draw should be less than 50mA (~30mA to be accurate) Thus the battery is fine and i have a current draw somewhere. Since the battery was under warranty, the dealer didn't charge me for the battery check service.

So i decided to isolate the failure by myself. I disconnected the negative lead on the battery and attached a multimeter in series. I only noticed a 750mA current draw (don't know how the dealer came up with 1.4A). Anyway, I started by disconnecting the power seat module (its the two switches located under the seat) for both the passenger and the driver side. The current draw remained the same (750mA). Then I removed the fuses in the rear SAM one at a time, and the current draw still remained the same.

The one thing left is the door control module. this seems to be a big pain in the butt to investigate. I don't really know how to start. Is there a way to disconnect the door control module without the need of opening each door and create a mess?

Also, what else should i be looking for. What could draw a 750mA draw?

Come on guys. I really need your help.

Thanks

 

By the way, I have attached the test log that the dealer gave me. It contains a lot of info. Hopefully this will help you "experts" to narrow down the issue. I see codes for the REAR SAM on page 2 that has to do with door control module (DCM). I also see stored events (on pages 4 and 5) for DCM-Front Left, DCM-Front Right, DCM-Rear left, and DCM-Rear Right. There is no way that all 4 DCM's are failing????

 

Any ideas?

 

Pull ALL the fuses one at a time till the current drops.
Thats the ones in the dash (did you know they are there?
Should be a chart in there too with which fuses do what..
left side of the dash, pop the plastic cover)
then all the ones in the engine area, and the one's in the back.

Spare fuses in the spare tire area, fuse pulling tool stuffed into the styrofoam by the rear SAM. Chart in the dash....you end up tearing the whole car apart to change one fuse. Ok, but your problem isn't the fuse.

 

Wow. I've never seen a printout like that, so I have no idea how many
individual errors are acceptable.
Most errors appeared to be stored, only a couple are current.
The only one that stands out to me, is the one on the first page that mentions a possible short....or open circuit.
Whats up with that? The 2 are quite different problems, and the system lumps them together. But it doesn't show as a now issue, STORED.

Pull the fuses.

 

C230 Sport Coup is correct...it's a fuse by fuse process.

This is what the draw should be for various components:

 

thanks guys. i've got the car in the garage and will start removing each fuse and check for current draw. I looked at the chart and didn't see any fuses for the DCM's. I have a feeling they might be the problem. Anyone know how to test them without ripping the door out?

Also thanks Splinter for providing me with this list. ~65mA should be the max draw with the car off.

Will find out in an hour or so if this is a fuse issue.

 

This can be as simple as a glovebox or under hood lamp remaining illuminated to a complicated problem with the CANbus failing to go asleep. The latter is the usual problem with the seat modules. They keep the bus alive and draw higher current than when asleep.

What stands out in the sheets (page 4) is the right front door sticking switch for the seat back. The switch is connected only to the door control module. The door control module "reads" the switch and sends information to the CANbus that the switch has been activated. The CAN then sends a signal to the seat control module, which does the grunt work and sends a voltage to the motor that moves the seat back to recline. The switch is mounted on the door, and has a wee bit of wire connecting it to the door control module.

Before I did anything, I would pull the door panel (how to is on the forum) and unplug the seat control switch from the door control module.

Pulling fuses one at a time might isolate the excess current draw to a specific consumer circuit, but then what do you do? The fuse only protects the wiring, and makes it easy to disconect individual banches of the electrical system. Some items don't have a fuse, like the CANbus. It operates at such a low current a fuse would not protect anything. Once you have better data, perhaps a more pinpoint check could be suggested.

Good luck.

 

Alright, Here's the latest updates on this issue. I checked all the fuses and monitored the current draw constantly. I believe I narrowed down the problem to an acceptable level. Below is a step by step of what I've done to isolate the failure. Hopefully others can also benefit from it if similar problems occur.

Step 1: Before disconnecting the Battery, I decided to disconnect both seat control modules (passenger and driver) since I've read that they fail at a high rate.

Step 2: Then I disconnected the NEGATIVE lead from the battery and attached a multimeter in series. This was used to measure the total current draw. First I observed a 1.8A current draw immediately after I attached the multimeter. After ~20 sec, the current dropped to 1.1A. After couple of minutes, the current went down to 105mA. This told me that the CAN is working fine and most components are going to sleep except maybe a minor component causing a 105mA draw.

Step 3: Since I know there should be ~30mA current draw with the car at rest, i decided to unplug all the fuses from the rear SAM (make sure you take a pic or write down the location of the fuses) and monitor the current. After removing the fuses and closing the trunk immediately afterwards (don't want any extra current to show on the meter) the current dropped to 15-40mA after couple of minutes (which was great). Then I started connecting the fuses one at a time until I narrowed down the failure to fuse #9 which was causing a 105mA draw.

Step 4: Kept on connecting and disconnecting fuse #9 and the results were always 15 to 40mA with the fuse disconnected and 105mA with the fuse connected. I kept the fuse disconnected and started plugging the seat control modules (one by one). I plugged the passenger's seat control module first and noticed no current draw after couple of minutes (it takes about that long for the CAN to go to sleep). Then I plugged the driver's seat control module and noticed a constant 1.085A draw, which means that my driver's seat module is defective .

Step 5: so with all the fuses connected and the power module connected, i obtained a total current draw of ~1.2A. I'm sure this was enough to drain the battery.

Step 6: To narrow down the problem with fuse 9, i decided to remove all the fuses in the front and rear SAM unit and the dash unit and kept fuse 9 (only fuse 9) connected. The current draw was a constant 100mA. I checked which component is using fuse 9 (using the fuse chart) alone and it turned out this fuse effects the following components :

1- Tilting/Sliding Roof
2- Rain Sensor
3- Make-up Mirror
4- Garage Door Opener (Which I don't use/have)

There are also other components such as Dome light, which require fuse 9 to be connected in order for the light to work.

Step 7: Didn't know what else to investigate, so I kept the driver's seat control module and fuse 9 unplugged until i figure out what to do with them.

Now the million dollar question is "What could be causing this 100mA draw that I'm seeing off fuse 9 and is this normal draw? What else can i do to further isolate this failure?

I'm also thinking in opening up the driver's seat control module and attempt to fix it myself. Did anyone attempt to fix the module and had success with it?

Thanks for the help so far. Hope to receive additional advise so that there can lead to a happy ending. Note that the sun roof and the dome lights are currently not working because I unplugged fuse 9.

 

By the way, I've attached the fuse chart for my car.

 

Good detective work. The rain sensor is on all the time. The four LED's in the rain sensor might draw 40 mA and an additional 10 mA for the radio receiver in the Home Link opener. I am confused as to why you don't think you have it. US market cars include the opener and rain sensor in the sunroof package. If you have three buttons on the bottom of the rear view mirror, you have it.

Your current draw of 105 mA might mean everything is OK.

It is not easy to repair the seat module. It is a surface mount assembly, and the processor and comm chips are not easy to buy in small quantities. There is a shop that repairs them. They get around $ 500. Not inexpensive, but less than the dealers, and a better warranty.

http://www.bba-reman.com/content.asp...Control_Module

 

Thanks Moviela,

What I meant is that I never used the garage door opener but i do have the 3buttons on the bottom of the rear view mirror and the rain sensor as well (by the way, how do you change that sensor?).

So you're telling me that a 105mA is a normal draw? From post #13, splinter shows a max draw of 66mA?

In regards to the seat module, nothing is easy to repair, but I would like to take a shot at it. I just need instructions on how to remove the unit from the seat, instruction on how to open it up, and if you have some schematics, that would be great.

 

Splinter's page is from April 97, and predates the W203. The rain sensor is part of the windshield, and is replaced with the glass. It is an optical device that is bonded to the glass. If you remove it, it cannot be put back properly.

Most modules are easy to remove, having a clip or some other easy to assemble latch to hold it in place. Some have a fixing screw. Usually Torx head. Opening them is also easy, usually some tangs and slots to contain them. Once inside there is complicated surface mount parts and clever connections holding things together. If you don't have a surface mount rework station, epoxy solvents, and solder creams, repair will be imposible. This assumes that you can get the components, and have the ability to flash the parts that contain firmware. The firmware is not available from Mercedes, nor are schematics or service data for the modules. Anyone hoping to service a module will need to de-engineer it, find the defect, and write or copy firmware if needed.

 

You're right. Splinter's page is old. This assures me that 105mA is a normal current draw. This also makes sense since a battery that is rated for 100A usually lasts 200 hours (9 days) on this 105mA draw. So the problem is solved and the issue is the seat module .

You're encouraging me to go ahead and open up the unit . I can get access to the rework station, epoxy and solder creams. This means that I can remove each chip on that PCB and replace it with a new one (that's only if I can get the IC's/chips, which is sometimes very difficult to obtain). One thing I don't know how to do is copy the firmware, and will that be needed to all chips or just the Flash chips?

 

Excellent troubleshooting. You went from a newbie without a clue to an
expert with the help of this forum?...pretty amazing considering.
A joy to read something intelligent and well thought out,
as well as educational.

Firmware is likely on a very small chip
Used to be firmware reader, burners sold for like 100 bucks....
but chip specific DIP, not surface mount.

 

unless the specific chip with firmware is damaged, there should not be any need to reprogram anything. Any chip (IC) can go bad and start drawing some current, but most likely that could also be more like a discrete component failure such as capacitors used to filter the supply voltage coming into the unit. They usually have some kind of internal voltage regulator chip also that can fail and leak,

Repairing that module goes way beyond the capabilities and resources of most participants in this forum. Try getting a used one at lower costs.
The companies that sell those usually give you a few days to check them out and return if their part is defective.

As a final alternative leave it disconnected until you can work it out.

 

Any advice on where to get used units? I need one.

 

A link to a forum where I put my diagnostic numbers.

You folks were a big help, thanks!

https://mbworld.org/forums/c32-amg-c55-amg-w203/230065-2002-c32-power-drain-battery-dead.html