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I have (had) an 07 SL550. Excellent maintenance history. No Mods of any kind. 43K miles. Spontaneously, in my garage, an electrical fire developed in the right front part of the trunk. It burned several harnesses and a control box of some kind and a large area around it. The trunk and the car filled with smoke, but the fire did not progress, probably because of lack of oxygen as the top was up and windows shut. Didn't discover it until the next day. Repair estimate was $21,400. Car was totaled and I await a check. No one will fix this car. Who knows what it did to the rest of the electrical system. Ironically, it started when I needed to move it into position for the tow truck. This is not an isolated problem. There are a couple of videos and several reports of EXACTLY the same thing. Mercedes must know about this. I loved the car and want another one, but am hesitant. Comments?
My wife has a 04 SL500 with 92,000 miles on it. Yesterday while parked in the garage for the last 2 days we had the same experience. Fortunately we were just about to leave in my car when we smelled the smoke. I was able to get the car started and out of the garage before potentially loosing my whole house. The engine would not shut off and appeared to be running at max rpm's. The headlights were on and flashing on the left side. The cockpit was full of smoke. I was able to manually open the trunk and disconnect the rear battery. That area was badly burned. Next I disconnected the forward battery. The engine was still raving at high rpm so I removed the air cleaner and smothered the engine to stop it. I will talk to my insurance man Monday but my mechanic thinks it is a total loss. What a shame. We have owned this car for 11 years and it has had excellent service. Nothing was spared in keeping my wife's baby in top shape. With this "common" problem with this model I question if I should buy another one.
Never heard of this issue, but obviously worth investigating.
What do you guys think about replacing the unit in question? Or is it battery related? I'd rather pay couple hundreds for a new unit than replacing the entire car...
Never heard of this issue, but obviously worth investigating.
What do you guys think about replacing the unit in question? Or is it battery related? I'd rather pay couple hundreds for a new unit than replacing the entire car...
I’m also curious about solutions to this issue. Can you just replace the unit and does that solve it? What about cutting the trunk liner around the unit and covering In something flame retardant. Looking for options because I am seriously considering an R230 purchase.
I have (had) an 07 SL550. Excellent maintenance history. No Mods of any kind. 43K miles. Spontaneously, in my garage, an electrical fire developed in the right front part of the trunk. It burned several harnesses and a control box of some kind and a large area around it. The trunk and the car filled with smoke, but the fire did not progress, probably because of lack of oxygen as the top was up and windows shut. Didn't discover it until the next day. Repair estimate was $21,400. Car was totaled and I await a check. No one will fix this car. Who knows what it did to the rest of the electrical system. Ironically, it started when I needed to move it into position for the tow truck. This is not an isolated problem. There are a couple of videos and several reports of EXACTLY the same thing. Mercedes must know about this. I loved the car and want another one, but am hesitant. Comments?
happened to me today!
I saw some smoke coming from the trunk area.. within 5 minutes the car was engulfed!
Much has been written here regarding the battery module that causes the fires. That module is in the front right trunk. I installed a Smoke detector in the trunk as part of my Alarm System to warn us when the car is in the Garage. A friend has his house burned down because of this module. Replacing it with a new one just in case has not been fully discussed here as preventive maintenance. Gene
Guys, after seen several posts on this issue, I think some necessary precautions needs to be in place. Definitely insurance could pay for the car, but the fire in our homes will be catastrophic. I am thinking of a thermo-sensor on top of that box, The sensor connected to an alarm system or a power relay to disconnect the battery. I will start my search for the solution and will share when available..!
The smoke detector Gene mentioned may also do the trick..! Gene what type of detector did you use?
Guys, after seen several posts on this issue, I think some necessary precautions needs to be in place. Definitely insurance could pay for the car, but the fire in our homes will be catastrophic. I am thinking of a thermo-sensor on top of that box, The sensor connected to an alarm system or a power relay to disconnect the battery. I will start my search for the solution and will share when available..!
The smoke detector Gene mentioned may also do the trick..! Gene what type of detector did you use?
I used the smoke detector brand that is in my house burglar alarm so I get emails and calls if it goes off. ( Front Point Security )
Guys, after seen several posts on this issue, I think some necessary precautions needs to be in place. Definitely insurance could pay for the car, but the fire in our homes will be catastrophic. I am thinking of a thermo-sensor on top of that box, The sensor connected to an alarm system or a power relay to disconnect the battery. I will start my search for the solution and will share when available..!
The smoke detector Gene mentioned may also do the trick..! Gene what type of detector did you use?
A temperature sensitive battery isolation circuit is pretty easy to do *in theory*.
Combine a temperature sensor module like this with a pair of 200 Amp battery relays like this, one relay for each battery. Mount the sensor right on the BCM, then figure out where to place the relays, probably in the trunk somewhere near the BCM, making sure to stay out of the way of the folding top. Fabricate some custom battery cables to route battery voltage through the relays. All in cost probably $150-$200USD.
I say easy to do *in theory* because I haven't assessed the battery cables going into the BCM, so I don't know how hard it would be to access and modify them.
Edited to add - you'd probably want some type of alarm as well - the temperature isolation circuit will remove power from the BCM as long as the BCM temperature exceeds the designated threshold, but once the BCM cools off power will be restored. So an overheating BCM would basically cycle off/on/off/on/etc. and you wouldn't know about it.
Bruce, I actually ordered one of the controllers, which I plan to set with the prove taped on the Module. Then I will get a + feed from the battery, routed to the NO controller relay and used a buzzer as shown. The buzzer supposed to yell at 100 Dba..! So, after finding out what would be the hottest the module could get after normal operating conditions, I will set up the controller to trigger 25% over the top value. So, if I ever hear that buzzer, will run to save the car...! The problem would be when I am not around, so, the relays you suggested will do the job, but it would have to be set in a way that when disconnected , should remain that way till reset! An interlocking control relays will do that job! Temp switch
Bruce, I actually ordered one of the controllers, which I plan to set with the prove taped on the Module. Then I will get a + feed from the battery, routed to the NO controller relay and used a buzzer as shown. The buzzer supposed to yell at 100 Dba..! So, after finding out what would be the hottest the module could get after normal operating conditions, I will set up the controller to trigger 25% over the top value. So, if I ever hear that buzzer, will run to save the car...! The problem would be when I am not around, so, the relays you suggested will do the job, but it would have to be set in a way that when disconnected , should remain that way till reset! An interlocking control relays will do that job!
It looks like that controller has a high temperature alarm function which turns off the relay above a set temperature, but it's not clear if it remains off when the temperature falls back below the threshold. This alarm function is separate from the normal heating/cooling thermostat functionality.
Here's the instructions I found for that controller, refer to section P7 Temperature Alarm Function....... like I said, it's not clear at all on exactly how it works, but I think it's saying that once the alarm threshold is reached it remains in alarm state until you press and hold the "-" key until the temperature setting reaches zero, then press once more to set it to "off". If this is true this would be a workable solution, in the case of an overheating/melting BCM you'd basically find your car with no power, but otherwise undamaged.
2005 R 230 SL350 (M112 3.7). Sold the 1966 W113 230SL recently
When the heat treshold is reached the unit should derive itself of power too. So if it has a NO relay wouldn't everything be 'dead' untill the owner turns up?
Having said that, I can see yet another source for defects loom. For instance, if the starter battery relay fails, you find yourself in a situation we all warn each other for - never disconnect the starter battery first...
Last edited by Frederick NL; 08-23-2022 at 03:06 PM.
Bruce, that kind of relay will not work because it is normally open so when activated close the high amp circuit. What you want is the opposite..NC so your battery is connected, then when temp reaches high value, it activates and opens the circuit. Also, those relays are for intermittent use. They will get hot in continuous duty.
One question I have is, which battery causes the module to overheat? Starter or Accessories? The starter has a fuse that will burn going to the module if overloaded! So, that leaves the rear battery!
I was thinking that a system using a permanent connection and a relay activated by the ignition will do the job since the permanent connection could be made using a 20 amp fuse, which will keep the dormant and the temporary circuits like the door opening compressor working...then when the ignition is ON the power relay will join the accessory battery with a high amps bridge. In that way, if a short occurs or the module starts heating up, the 20 amps fuse should trigger and prevents further battery current draw!
These and another type of thermal extinguisher just have appeared in my searches. Don’t know how they work, but would like to know what is causing this problem. Not a great fan of this particular issue with this car snd the frequency it has happened. Getting the trunk opened in this sort of situation even if you are in close proximity may. Difficult at best.
It seems ridiculous to me that such a widespread, dangerous, and catastrophic issue (that has spawned many threads from the many people it has happened to on this forum alone) has not triggered a proper investigation and recall from Mercedes-Benz. Has anyone figured out the root cause of the module failures and fires?
"Suspect Battery Control Module (BCM) - Investigation underway"
This isn't the first time someone has tried to figure out the root cause, though I hope this attempt will get somewhere. Mercedes-Benz and their suppliers are the best equipped to identify the root cause (given they have the technical details of the design and information about cases worldwide) but I have not heard of any investigation attempts by them. Usually I see recalls happen for much rarer and less catastrophic issues than the battery control module fires that pop up on R230 forums regularly.
Ok, guys, here is what I did to have peace of mind and avoid burning the car and home..!
I used a Normally Closed heavy duty relay connecting the auxiliary battery to the ground. Then used a controller to sense the temperature of the ECM and set to 250 F. The power consumption is very minimal. The way it works is: When the controller senses temperatures over 250 F, its relay actauated the Normally closed heavy duty relay and opens the circuit so the auxiliary battery is disconnected from the system and buzzer activates intermittently. When it cools down connects, heats up and disconnect again, unless I use a latching relay system that once is activated it stays that way, instead I used a buzzer!
08-03-2020, 10:38 AM
