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I ve had almost same issue. But while turning car off. As soon as i pushed engine off, all dashboard lights came on. I could not lock the car and did not test anything else but turned on the car again. Then everything got back to normal. I did not drive it yet, tomorrow i will check again. I have lately replaced auxiliary battery, main battery is 3 years old.
IS main battery feeding all except gearbox which is fed from auxiliary battery?
The issue for mine ended up being the CAN Bus Terminal, these are located under the kick plate next to each seat, right under where the door closes. What happens is the drainage system in the car gets clogged with debris causing rain to drain in the car instead of draining out of the car. It pools up under the carpet where these terminals are causing short circuits between the SAMs. I dealt with this issue for years, with a lot of help from good people here, it was self diagnosed and fixed that's why I'm replying to pay it forward. Hope this helps.
I ve had almost same issue. But while turning car off. As soon as i pushed engine off, all dashboard lights came on. I could not lock the car and did not test anything else but turned on the car again. Then everything got back to normal.
I did not drive it yet, tomorrow i will check again. I have lately replaced auxiliary battery, main battery is 3 years old.
IS main battery feeding all except gearbox which is fed from auxiliary battery?
What AUX batt can power depends on what size it is. They went from Small to Medium then to Extra small.
Normally the whole car exclusively feeds from the alternator including the transmission controller.
-- The small in dash AUX is said to help shift gear selector under extreme conditions.
-- The medium in trunk AUX is used during ECO restart to power the car reduced load while Main cranks the 600A engine starter.
-- The tinny AUX in footwell is a 4. Farad set of capacitors instead of prior lead-acid batteries.
The eye opening Christmas tree sounds like a perfect example of a glitched car network.
You should scan your car in hope to see what module got soft-crashed.
As soon as the VIP's get a chance to sleep (power cycle ie. Reboot!) the car is ready like nothing happened.
The remaining upset modules are SAM for which you'll want to disconnect MAIN + AUX Batts before Main gets drained down.
Last edited by CaliBenzDriver; Oct 5, 2022 at 08:34 PM.
The issue for mine ended up being the CAN Bus Terminal, these are located under the kick plate next to each seat, right under where the door closes. What happens is the drainage system in the car gets clogged with debris causing rain to drain in the car instead of draining out of the car. It pools up under the carpet where these terminals are causing short circuits between the SAMs. I dealt with this issue for years, with a lot of help from good people here, it was self diagnosed and fixed that's why I'm replying to pay it forward. Hope this helps.
Yes! This is what I've been looking for. I've had the same issue with water. Is this why the mechanics are telling me they are getting all these electrical codes? Please tell me how to fix?
I am not a DIYer, unfortunately. I'm a retired social worker trying to keep my car going.
Thank you for all this information, yes I bought a used prefuse box and still have the same issue. I have a picture of the old one below to show the difference in mine and the one you are showing. Notice the relay plugs come out the side and the four single wires at bottom go straight in (not horizontally). I tried to removed the relay (A0035420019) with no success, you can see it has a similar diagram on it like the one you just showed me. Is this the same relay you are referencing? You can see I completely destroyed the prefuse box in this picture trying to take out the relay so this cannot be re-used. I still have the one in the car and can work on that one, do I have to remove prefuse box from car to test voltage? I really appreciate your assistance here, I have a friend coming over tomorrow with a voltage tester to follow your instruction.
How did you actually remove the yellow plug on the side? I cannot get it unplugged to save my life and no idea what kinda plug it is
i know this thread is very old by now but i had to say, THANK YOU!!
This helped me fix my car that not even shops could diagnose, 50 bucks later for a used prefusebox and problem solved!
People who are having problems like these, just take your time if you dont have competent shops near you! I was recommended to replace a fuel pump!!!!!
i know this thread is very old by now but i had to say, THANK YOU!!
This helped me fix my car that not even shops could diagnose, 50 bucks later for a used prefusebox and problem solved!
People who are having problems like these, just take your time if you dont have competent shops near you! I was recommended to replace a fuel pump!!!!!
What were your symptoms and what did you end up replacing?
i know this thread is very old by now but i had to say, THANK YOU!!
This helped me fix my car that not even shops could diagnose, 50 bucks later for a used prefusebox and problem solved!
People who are having problems like these, just take your time if you dont have competent shops near you! I was recommended to replace a fuel pump!!!!!
> You've fixed an issue ONCE with your PreFuse...
PreFuse does not randomly eat fuses... extreme currents do!
> You best need to find out WHY ahead of the same event happening again.
> The electronic modules in these cars adapt poorly to unstable swings.
> Tips To Keep Things In Check....
--> TIP 1: Use CTEK float charger to prevent drained MAIN/AUX batteries getting toasted with extreme charge currents.
--> TIP 2:Monitor voltage + current while driving with the car IC Display.
AGM batteries are really tough, to some extent.
Last edited by CaliBenzDriver; Jan 13, 2025 at 11:55 AM.
Well indeed my aux battery was dead but idk if the reason was the prefuse going bad or the age (it was the original one dated 2014). So i repalced that before i discovered that prefuse box is defective. After i replaced the fusebox and took apart the old one and tested all the fuses wich were okay, my problem was with the quiescent power relay which it would not turn power on circuit30g. I did not write my story but my problem was VERY intermittent. I also kept an eye on the alternator for sometimes wich was normal 13-14v with car running(although that was from the voltage reading in the cluster). It's been a few months now and car is great!
Thanks for the tips i do appreciate them!
Great people make these forum great!
Cheers
i know this thread is very old by now but i had to say, THANK YOU!!
This helped me fix my car that not even shops could diagnose, 50 bucks later for a used prefusebox and problem solved!
People who are having problems like these, just take your time if you dont have competent shops near you! I was recommended to replace a fuel pump!!!!!
Sounds like K2 relay inside F32 have it contact point pitting and/or its magnetic coil weakening thus poor contact and can develop intermittent contact.
K2 relay is the only "consumable" component inside the F32 prefuse box. Supposedly up to 15,000 latching/de-latching life cycle if that is a Hella unit.
The other one V19 Q-Diode start stop relay is solid state unit, will live a longer life usually.
Anytime you open your door or trunk, K2 will activate. So K2 working life is not merely during engine running.
As our car is aging, K2 will someday go bad and including all the constant* ON relays ( *door open, accesories mode, Ignition mode and engine running ) at Front and Rear SAMs.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by mcspecialist
The issue for mine ended up being the CAN Bus Terminal, these are located under the kick plate next to each seat, right under where the door closes. What happens is the drainage system in the car gets clogged with debris causing rain to drain in the car instead of draining out of the car. It pools up under the carpet where these terminals are causing short circuits between the SAMs. I dealt with this issue for years, with a lot of help from good people here, it was self diagnosed and fixed that's why I'm replying to pay it forward. Hope this helps.
Water intrusion is like poltergeist in your car. It causes all sorts of fleeting problems. My solution is to remove the plastic plugs in the floorpan in areas where water will puddle. The holes are above the undercarriage splash pans, so they are somewhat protected from dirt and water.
All warning lights on, car starts, gear will not engage, no infotainment working, windows work, boot can’t be opened, coolier fan runs at full speed with cold engine.
After reading all here, and the linked information as well, I figured it is the auxiliary battery that is dead on my 2012 SL. It would make sense. Replaced the starter battery which was all dead, then the aux battery. It worked - but the issue returned next day.
An MB specialised workshop quickly found the fault to be a relay that has as its only function to shut down all electrics after the car has been switched off for 6 hours. And to switch everything back on when the locks are opened or car started. But aa it is now faulty, it switches back on only occationally, so you can be left anywhere, I had to have the car towed to the garague.
This particular relay is not separate, it is built into a fuse box, into the box structure itself, so the 630EUR fuse box needs to be replaced. There was one left in Europe, it will now become mine…
All warning lights on, car starts, gear will not engage, no infotainment working, windows work, boot can’t be opened, coolier fan runs at full speed with cold engine.
After reading all here, and the linked information as well, I figured it is the auxiliary battery that is dead on my 2012 SL. It would make sense. Replaced the starter battery which was all dead, then the aux battery. It worked - but the issue returned next day.
An MB specialised workshop quickly found the fault to be a relay that has as its only function to shut down all electrics after the car has been switched off for 6 hours. And to switch everything back on when the locks are opened or car started. But aa it is now faulty, it switches back on only occationally, so you can be left anywhere, I had to have the car towed to the garague.
This particular relay is not separate, it is built into a fuse box, into the box structure itself, so the 630EUR fuse box needs to be replaced. There was one left in Europe, it will now become mine…
I hope your new Prefuse restores sanity. I don't quite understand why new K32 will help batteries not drain...
A rogue module is keeping your busy chassis awake... did solid state relay get toasted into short-circuit on battery jump?
Preserve your batteries by using a battery tender until this is working.
Last edited by CaliBenzDriver; May 25, 2025 at 03:06 PM.
In the N93 module ( inside front SAM , but Central GateWay and not the N10/1 ), there is a BUS AWAKE information.
I suggest to take a look at it too, as to why K2 relay at F32 did not go to sleep past 6 hours.
6 hours is its max limit when car not in use, all 4 doors and trunk closed.....hood can be opened and stay opened, no issue.
Bom dia, queridos amigos. Tenho uma oficina aqui no Brasil e chegou um W204 com o seguinte defeito: a caixa de fusíveis está desarmando e não envia energia positiva para o módulo SAM traseiro. O motor gira, mas não pega, e a bomba de combustível desliga. Desmontei a caixa e resetei o relé manualmente; o carro funciona normalmente, mas de um dia para o outro o fusível desarma sozinho.
Já removi o sistema de som
que o antigo dono instalou, e o problema persiste. Agradeceria se alguém pudesse me enviar o diagrama elétrico ou, se alguém já se deparou com um problema semelhante, poderia me ajudar.
Estou usando o Google Tradutor, então peço desculpas por eventuais erros de ortografia.
Was the tow covered by the dealer or MBUSA since you had it towed to them? This is usually the case if you call MBUSA ROADSIDE ASSISTANCE even if your vehicle is out of warranty.
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THANKS
