Major electrical fault A207

[Benzodiazapine]

My 2014 E class Cabriolet (A207) had a weird electrical fault today. Started up this morning and the Comand system was dead and I had 13 fault messages, all back lights dead, both front airbags dead, parking assist dead, usb charging port dead etc. Obvious assumption is that these all share a common power root so maybe a major system fuse or some relay or other module??? Any thoughts ? Bob

 

[Blobcat]

Hello and welcome

What’s your battery voltage?

 

[Srdl]

As above Bob. May be due to low or irregular battery voltage. Mercedes systems are notoriously sensitive to low voltage and recent cold weather and less lockdown usage may be the cause. Try charging the battery overnight first perhaps?

 

[Benzodiazapine]

Thanks guys I will put it on a trickle charge tomorrow and see if that clears it, I will report back.

 

[Benzodiazapine]

Ok I trickle charged it overnight but it hasn’t made any difference , battery is showing 12.8v on the multi meter when off and 14.76v when running,any thoughts about it being a pre fuse? Systems that are gone offline include all back lights, both front airbags, air scarf, Comand, park assist, and probably a few other things, car starts and drives ok apart from that. I’m seeing other articles citing similar situations being caused by a relay or a pre fuse. Any thoughts?

 

[ajlsl600]

Would have thought airbags controlled by ,if need be ,both batts ,safety?
Check codes for lots of under voltage errors if so suggests batt on way out. Note all codes,descriptions before deleting .
Wud be nice IF smarty car,not ,put up message saying batt goosed, instead of sending u to £100plus dealer coffee experience.
Good luck.

 

[Benzodiazapine]

OK..so I seem to have fixed it but Im not sure how!. I went into the front fuse box (under bonnet, drivers side) and pulled every relay, tapped it a few times and pushed it back in, I then did a continuity check on every fuse, and the three large heavy duty 50amp fuses I pulled each of them and inspected and pushed it back in, I then got into the rear fuse box(which on the cabrio is is the spare wheel well on the RH side) and did the same stunt there.(that's also the location of the auxiliary battery and I did a voltage check on that, it was showing 12.8v).Then I did a regular start up and everything was working again. My best guess is that one of the relays is dicky, and when I fiddled with it, it "found Jesus", ....at least temporarily. I was very concerned that one of the massive pre-fuses was blown and I might have to replace an entire pre-fuse module but that now seems unlikely since blown fuses don't unblow. I suppose it may go wonky again but if it does I will at least know where to start looking. thanks for the advice and I will report back if there are any further developments.

 

[mioba]

Good stuff. obv a sticking relay.