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(edit)2012 C300 4matic- intermittent cold weather MASS electronic failure
Hey guys,
Long time lurker here, finally needed some 1 on 1. Over the past 3 days i've encountered the following issues.
-7 Mar 2016- 5:30AM- temp 29F - 2012 C300 4MATIC-5XXXX mi Engine turns over and car starts. Headlights are on
Interior lights fail to turn on.
Center console lights, shifter lights, COMMAND system all dark.
Electric seats fail to move.
Electric trunk will not open.
Dash monitor is ON and displaying the following errors: General SRS malfunction Front left SRS malfunction Front right SRS malfunction Collision Avoidance System Malfunction ABS malfunction Traction Control Malfunction
Radiator fan operating on HIGH (its cold?)
There are a few other errors that show up. Will update when i get home.
So the car started up fine and everything is working when i arrived home at 2pm temp 54F.
-edit removed assumed SRS failure as culprit
-8 Mar 2016- 5:30AM - temp 30F
Same problem as yesterday.
At around 8am i turned key, and everything stared up fine. Will get load test done on battery as recommended by forum member.
Battery was reading 74% ah, proper voltage. Decided to replace. Everything "seems" to be fine.
-9 mar 2016- 5:10am -
IT HAPPENED AGAIN
So, it appears that it wasn't the battery. I'm not leaning towards a grounding issue perhaps? I'm going to hook a space heater inside the garage to keep the vehicle warm throughout the night. If the problem doesn't replicate, could it indicate a grounding issue? a wiring issue? The cold is the common variable here. What could that indicate? I've never had many car issues so i'm not very experienced in diagnostics. Especially intermittent ones.
Other ideas-
Voltage regulator?
ECU?
Something stupid?
Any thoughts, ideas, or gut feelings would be so extremely appreciated. I feel this is a problem I can solve without a dealership, but I don't think i can do it without all of you!
-cw
Last edited by Willybob; 03-09-2016 at 02:11 AM.
Reason: Day 3 issue, new information, new insight
So, 8 hours later. Buddy dropped me off at home. Turned on the car, and everything is functioning normally. Any ideas as to what could be the problem? I'd hate for this to happen at a bad time. Murphy's law and all that.
Will do. I'm over In Germany right now, things are a bit more expensive. What am I looking at for a new battery?
So, day 1 the problem fixed itself. Day 2 it happened again in the morning when the temp is below freezing. Load tested and replaced battery. Day 3 the problem has recurred. Anyone have any thoughts? I'll probably go into the dealership soon, but I'd love to avoid the 200$Ish diagnostic :/
I had the same issue, mine ended up being the main fuse block under the hood. This is all internal the one that you hook the battery charger to. Cost my warranty company $1100 at MB dealership to fix
Leaning towards what superjet already said. I've had this issue a couple times on the 204's. Prefuse box on the left side. It's a non-serviceable fusebox. There's a quiescent current cutout switch in there that goes bad and basically that prefuse sends power to major control modules. It will throw a fault code on xentry, possibly on generic scanners but probably would just show the code and no description, however can not confirm as I haven't tried.
Man that's unfortunate. It's strange, a few weeks ago I had taken my vehicle to Bosch here in Germany. They said it was the battery, and trickle charged the thing for two days. Afterwards I havnt had the problem untill yesterday morning. I went almost two weeks with it being okay, and it just happened again. Should I buy a fresh battery? I'm really at a loss, I'm no longer under warranty unfortunately. I'm at about 56k miles.
Edit- to be clear, I had replaced the battery once already, but Bosch said that it wasn't the right one and charged my factory battery to full and installed it.
If the battery tested bad replace it. Undervoltage is a killer for control modules. If the batteries questionable, do a stress test. With the car off turn on the hazards and let them flash for about 20-45 minutes, I've heard 15 mins is good enough I've also heard run it for an hour. Test the battery again. This should let u know how healthy your battery is.
Here's why I don't think it's the battery, the components that you are seeing inop are apart of a consumer shutoff program when the rear sam either sees an open quiesent shutoff relay in the prefuse box or battery voltage below 11.5 volts with key off and consumers on such as comand on and doors open, this is so you'll be able to start the vehicle and recharge the battery. However when the key is cycled rear sam wants the okay to close the relay and bring the modules back online, in your case some are some arnt. The key here is you can start the car so you have power to ME, DRIVE AUTHORIZATION AND headlights operational so you know the front sam is working, but still no SRS. Also the engine fan is roaring away like a fighter jet which is straight power from prefuse, it also draws a lot of current so with a bad battery the ME wouldn't want to stress the charging system unless there's some failure. Also most components controlled by the rear sam are still inop. Wiring diagrams and gf documents from startek could explain this in full, if you would like more info let me know. I'm only giving a suggestion based on previous experience and knowledge about the system as your car might need some other component to fix the issue. But I'd definitely look into that prefuse box.
Hey mbtech, thanks for information. I replaced the battery once again with an exact copy of the factory. Everything was dandy for about a week and last night the problem reoccurred. My question is, how is it possible that the prefuse is causing this problem intermittently? I don't question your expertise at all. Just trying to make sense of the issue. I can tell when I open the door if it's going to happen or not, the interior dome lights fail to come on. Problem occurred last night, but not this morning.
I know someone up top said the box was 1100, I've seen a few online for much less. Should I get it from the dealership or buy online and have an indie do the labor? Possible to DIY? Additionally, does anyone have the part number?
Sorry for seeming so needy, I'm in Germany on a mil assignment,and the language barrier with technicians here really hurts the process.
Last, is there any further troubleshooting I can perform and report to you guys that can rule out other options other than the prefuse box? Confirm its Underneath the positive terminal?
No worries man I completely understand. Too bad it wasn't just the battery. The prefuse box is laid out with power wires coming in and power wires going out with internal non-serviceable fuses. There's also a 4 pin connector that goes to the cutoff relay. It's actually the relay that's failing, as I've already explained. You could check powers and grounds at the prefuse which should be 12v power and 0 ohm ground.
Unfortunately electrical diagnosis is one of the most difficult things on these cars if you don't have access to xentry, starwiring, or wis. There will be a fault set in a short test. I recommend taking to a dealer and paying the diag for them to scan in. If you wanted to risk it to get the biscuit, the prefuse box is easy to install with I believe a few sockets, 8/10/12 maybe 13mm. All the wires have tabs on the ends to only go in one location so itd be difficult to mix them up. The hardest part is unclipping the the prefuse from its mount on the side of the bulkhead.
As for the part number I can get it, there are just a bunch of option codes that need to match your vehicle. I'm sure the 1100 price was including labor as we usually charge diag plus a couple hrs to install it. I don't believe any programming is involved.
Hi, I just grabbed new prefuse box from dealer. I know I've read it's fairly easy to install but I would love some guidance. Is anyone able to provide some instruction at all . Or any tips . Thanks in advance
From memory, the tricky bit is loosening all of the attached cables to make sure you can comfortably pull the prefuse box out (with most cables still attached) and then basically move the leads over to the new prefuse box. Worth being patient as some of the cables are small and could be damaged, certainly if you use any force. I was struggling for a while to get the old unit out and then realised if I undo a bracket on a air con pipe that made all the difference.
Rough steps are:
1. Remove battery and battery tray.
2. Remove all cables connected at the top of the old prefuse unit (take a photo of it first just in case you need to refer to it later!)
3. Remove bracket to air con pipe which runs alongside prefuse box - it will be obvious which one - just allows the AC pipe to move an inch or so out of the way. If not obvious, leave it and see what's obstructing you later on.
4. You may need to snip a couple of zip-ties that are coupling the cables (below where the battery tray was) that allow the prefuse box to come out further.
5. You'll have to play the rest by ear - disconnect any cable you have to, but otherwise be patient and try to tease it out! If you refer to the new prefuse unit, you'll notice a lug/clip on the bottom - this retains some cabling and you may need to loosen these cables on the old unit which is a little tricky.
Once you get the damn thing out it's really easy - just reconnect the battery. Nothing else you need to do.
I need to replace the contact of pyrofuse. You said "the hardest part is unclipping the prefuse from its mount". I 100% agree. I tried every way I can think of but no success. Can you explain how I should do to unclipping the profuse?
Here is the advice I got on unclipping: take a screwdriver and pop the orange part(locking tab) up a few mm, don't fully remove it. Once that's unlocked just wedge off the connector from the prefuse.
Hopefully this thread still has a few active viewers.
I'm starting to wonder if my pre-fuse apparatus is also starting to fail. I'm started to see irregularities with the heat, including the outside-temp sensor reading a steady 75F, and my code-scanner has a stored "under-voltage at 30g" message. I've also got the aforementioned quiescent current error. I'm wondering if anyone "in the know" might be able to tell me if a faulty 30g relay (prefuse component) could potentially lead to the Audio/COMAND cutting out when it's very hot?
I may have already jumped the gun on this question, but in referencing 30g, am I correct to assume that "circuit 30g" is this pictured below...
03-07-2016, 02:36 AM
(edit)2012 C300 4matic- intermittent cold weather MASS electronic failure
