W204 Electrical Systems Issue

[BonfireMike]

Hi all,
Long time watcher, first time poster as such and really hoping I can get some help here, feeling pretty on edge that I’ve somehow caused some big damage to the cars electrical system.

2014 C250CDI, I’ve previously added a CarPlay retrofit system which works great. Today I was adding a 12v socket on to the CarPlay loom for a <1a accessory, to switch on/off with a 12v ignition switched line, off the CarPlay unit. It has a spare line for this as well as a ground, so no issue here.

All working great when connected but not with panels refitted. Refit panels, went to final test and car is in a world of pain.

Traction control icon and ‘inoperable’ showing on dash, then tyre pressure monitor system inoperable, then headlight auto full beam system inoperable.

In addition, the interior lights were dimming on/off, the HVAC switches on for a few seconds, off for about 30 then repeats, headunit buttons do the same, however no sound nor does the screen light up. Probably some other things I’ve not mentioned, but safe to say the car isn’t have a great time.

Engine does start, however may need one or two goes due to the inoperable error. Indicators also don’t seem to work overall, however full beam manually does, so really not sure what’s on.

Radio and command fuses in the boot and engine bay are fine, but trying to think if there’s one on the back of headunit.
On that note actually, some of the errors seem to calm down after a few minutes, however when you press the on/off button on the headunit, it seems to set all the errors cycling away again, so I’m wandering if it’s something with the COMAND system?

Equally wandering if I’ve shorted something, as although unlikely, it is possibly I could have shorted the 12v switched line with the ground on the back of the CarPlay unit, but would’ve thought that would blow a fuse.

So, any help at all that I could get, I really would appreciate it so I can take a look and hopefully get this fixed.

Thanks in advance for your help!

 

[Jobsworth]

First thing I’d do is retrace your steps

 

[BonfireMike]

First thing I’d do is retrace your steps

Thanks for the quick reply! I’ve had a quick look at that, I’ve effectively undone the addition of the socket and checked I haven’t knocked any connectors etc. and it all seems ok, but I will probably fully remove it to be 100% certain.
Is there a chance a low battery could’ve caused this? I don’t think this is an issue as it’s only about 5.5 years old and gets plenty of long drives, but worth a consideration.
Thanks for your help.

 

[BonfireMike]

First thing I’d do is retrace your steps

Ok, went one step further as such and removed the kit I put in a couple of months ago and as soon as that was gone, everything was good again, bar an EML light staying on, so I suspect I may have totalled the CarPlay box, but I’d rather that the the car electrics!

Would not have thought it could impact on the car electronics that much!

 

[Jobsworth]

A few years back a customer presented me with an E39 BMW 540i which had a weird electrical fault. It would start ok, but then slowly loads of things would stop working or start working erratically. The indicators would work, but with a delay of about five seconds from what you did with the switch. Wipers the same. Something was crowding the canbus with erroneous talk, slowing everything down, eventually to a halt. We traced the problem to an ipod interface plugged into the back of the head unit. As soon as the offending box was unplugged normality was resumed. It’s amazing that a small thing can cause a world of problems

 

[BonfireMike]

A few years back a customer presented me with an E39 BMW 540i which had a weird electrical fault. It would start ok, but then slowly loads of things would stop working or start working erratically. The indicators would work, but with a delay of about five seconds from what you did with the switch. Wipers the same. Something was crowding the canbus with erroneous talk, slowing everything down, eventually to a halt. We traced the problem to an ipod interface plugged into the back of the head unit. As soon as the offending box was unplugged normality was resumed. It’s amazing that a small thing can cause a world of problems

Yeah, really is not what I'd have thought likely, but there we go!

This could be completely off the mark, but my only thought is that the headunit has the fibre optic going through it, and where the power to it seemingly wasn't getting to it, certainly not in the usual way, the rest of fibre optic communication link was broken as such and everything got thrown out.

No idea if that's possible or if the fibre optic is like a fail safe, i.e. if one part goes down the rest still works, doesn't particularly matter, but can't help but speculate.

Thanks for your help!

 

[Jobsworth]

The E39 puzzled me for a few days. I could communicate, albeit slowly, with every module on the bus. It was like a small child was shouting “me, me, me, me, me...” all the time, with all the other traffic trying to get a word in. I literally looped out the bus from control units in turn until the fault went. Headunit was the one, not the first I tried, not by a long way. I swapped the head unit for a known good unit, but it was just the same. Puzzled, I dug further and found a box behind the dash. It was called an Intravee if memory serves. Had gone round the twist. Sometimes it’s the smallest thing that takes the longest to find

 

[Deleted member 149005]

Was it MB OEM carplay kit?