Hi all, any insight would be appreciated.

myself and a workmate have been trying to get this car fixed with issues starting around 6 months ago. What used to be a periodic issue has become more and more frequent. Have had multiple mechanics opinions to help guide in the right direction.

when turning on the car, it will often start just fine with no issues and get wherever I need to be. However occasionally (usually seems to be after I’ve parked and jumped back in the car within an hour or two) I will be greeted with all kinds of errors. TCS, ESP, Cruise control, windshield wipers and headlights will all be not working. Sometimes it can be fixed by simply taking the key out, flipping it and starting the car again, however this solution has been working less and less, to the point where I’ve just had to drive the car home with all these systems down. It will almost always start. However a few days ago the car also would not start as well as all of these issues. I got it to start after about 15 minutes of flipping the key and trying to start (no crank) however upon pulling out of the park I was in, the car died out. I placed it back in park to try and start the car. After a few more key flips, it started, with all the issues, except this time it was also stuck in park. I then once again sat there flipping the key for another 15-20 minutes where I finally got the car started and without any error messages, driving back home as the car should.

I have spent hours upon hours looking over the car for anything I can see, as well as time in forums here and everywhere with a spec of information.

I’ve changed the key battery, car battery and ensured everything is plugged in properly. No blown fuses or relays as far as I can tell, no auxiliary battery errors come up either.

the closest sounding issue I’ve found is the 30G or F32 issue some have described (involving replacing the prefuse box) however my issues seem a lot more intermittent and slightly different given I can 95% of the time still start the car and shift to out of park (however usually with the errors mentioned before) most mornings the car starts just fine with no errors, but with a trip to the shops, I’ll get back in and usually have the errors all over the dash.

Any guidance would be greatly appreciated.

 

Sorry to read about your standard troubles with no fix. Can you enumerate what parts have been replaced already ?

Why don't you also report the current fault codes.

You want to float charge your battery and drive with headlights turned ON. This will prevent any aggravations caused by uncontrolled ALT voltage.

Cost: free + Time :10mn = Good Benz ownership

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All I’ve replaced so far is the battery in both the key and vehicle itself, old battery didn’t have any issues but thought I’d swap it out anyway. Alternator voltage seems fine as tested with a multimeter with car running, battery sits between 12.6 and 12.8 volts with engine off depending on how long it hasn’t been started.

I only have a Foxconn OBDII Scanner which shows no codes. I’m keeping my eye out for a local Mercedes specific scanner.

Ive been trying to get the car to show the errors again today but haven’t been able to yet. I left the battery unplugged overnight to drain all systems (no idea if that would help, just running out of options at this point)

Doesn't seem to have any mechanical issues as far as I can tell, even though it is quite high in kilometres at 250,000km’s. It did seem quite overfilled with oil when I purchased it however which was causing a lot of excess oil through the PCV valve, through the turbo and leaking out from the connections to the intercooler (these have all been fixed since) I’m unsure if this would contribute to any of these issues.

im currently awaiting a reply from the previous owner on anything he may have replaced.

also thankyou for your quick response

*EDIT* previous owner has just gotten back to me and stated he had replaced the starter motor, sunroof gearbox and plastic fuel pump surround which had cracked

 

Your Xmas Tree disruption needs some evidence to find its cause.
Do you know how to display battery vitals on your instrument cluster display ... voltage/Amps change during driving cycle. You want to capture the values by iphone camera or pen&paper

 

Sure can, I’ll grab those values shortly

 

yes please but not shortly, a normal drive is more significant!

You need to go about normal driving cycle and note what voltage is present and what current the battery is absorbing.

Voltage level is managed into multiple different phases.

What you're interested to see is what happens when ECU tries to command 12.6Volts

This is when it goes into frying mode yoyo with 90Amps through prefuse... the failed ECU control then forces ALT to drain the main battery = high energy power = high heat !

 

Alright Cheers!

Ill be going for a fairly long drive today, ill take note of where the battery is sitting at various points of the drive and post back ASAP

 

I did just want to quickly add, the car had the same issues with the old battery that persisted almost immediately still when the new battery was put in

 

Yes, I totally agree that rushing to replace the system battery is of no use when the problem is else where... such as poor ECU control of ALT below 12.3V.

I think we don't yet have evidence of what is causing your MB failure.


Two helpful procedures for you in the road, no tow truck necessary :

1-- If W212 car voltage goes below 12.3V turn on headlights to get a good 13.7V without any Mercedes struggles.

2-- When W212 car displays "XMasTree" display while driving, park it ASAP, then stop engine and restart after 5mn. All good for the next 30mn.

 

Hey guys,

sorry it took me so long to get back, it’s been a busy few days. I’ve had a proper scanner put on the Mercedes, which gave me 30 odd error codes of basically every electrical system failing at some point (this I knew) most notably however, there was a > 7.5v issue on the 15R and 30G circuit. Which from my understanding can cause a myriad of issues like I’m having.

driving the car for about 30 mins showing the battery info I noted these numbers.

cold start (lights on, radio on, aircon on, sat in the car for about 10 mins getting ready)
11.9v
upon starting the car it quickly started showing 14v then after a minute or so of driving went to a maximum of 14.6v, then going no lower than 14.3v over the course of the drive being about 30 mins and 10km (lots of red lights)

 

Good for you.... seems your alternator is proven good.

Your progress is going to be limited by lack of information on the 30 faults encountered. Some of use can guess the usuals troublemakers. Evidences always trump guesses.

It's generally a bad habit to discharge your battery with ignition off. From there you are guaranteed to get low voltage while cranking... nothing likes that. So much so ECO cars use a second battery to prevent VIP Modules from crashing during low-voltage crank.

In a nutshell your issue may simply be due to user error.

AMZ Keywork: "CTEK battery float charger"
✌️

 

It’s been having the same issue with a new battery, and the current battery regardless of jumping straight in and turning it on, I only mentioned I sat in the car for 15 mins because I had some emails to send and simply forgot to turn the engine on, this is not the issue and I’m certain it’s not user error. From everything I’ve researched it could be the Prefuse box, could this be a possibility? Regarding the 15R and 30G circuits having less than 7.5v at times

 

This is from my E400, but most W212 is very similar across models for its basic electrical..........






Yes, please check F32 prefuse assembly. I hope it is not the K2 relay having burnt/carbonized contact

 

Yeah, get the fault codes retrieved with English descriptions else round robin

7.5V is bad news at any rate.

When you note running voltage, don't forget the corresponding CURRENT Amperage info. There's a world betwen 90Amps, 40Amps, 30Amps, 8Amps and 0.Amps for the lucky few.

As far as prefuse box: it's a stack of heavy links with a Solid State MOSFET transistor... it's fairly rugged. One thing that nukes it is 90Amps

Overall we can agree your issue seems to involve low voltage.
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I have a question about the f32 prefuse box. when i check for continuity on the 3 studs on top I'm getting a tone on all but the main one. Should'nt they all be seperate from one another like Ig1 should be connected mg2. and im1 should be connected to mr8 and mr3 mr4 mr6 mr7. because if one of those curcuits had an issue like a voltage spike it would dammage all the other stuff maybe before blowing the fuse it is linked to. am i right.