[palmyra08]

Hi,

I ended up having a worrying electrical puzzle, with a 2008 E90 Saloon - and as local garages all want to send one to "specialist", any tips hugely appreciated - I am very afraid latter would poke around for N very expensive hours and change X things as usual, and maybe without success.

The key symptoms: foot well, radio button (but not the LED display and not dashboard) lights, parking, (flashing) long beam and reverse lights all randomly flicker *in sync*, but:
- foot well lights and radio button lights ONLY start flickering if at least parking lights are turned on,
- flickering happens also when not started engine at all (so it is NOT alternator and NOT vibration related),
- battery is well charged, computer even decides to do auto stop/start with current charge levels,
- radio itself, cigarette light holder charging, CD player, xenon headlights not affected at all and no flicker or hearable effect on radio for example.

Flickering went away for some weeks, then came back, and could not find weather or temperature correlation either... it is just utterly random but happens all the time.

Thanks in advance for any ideas / clues! Not even sure if soon upcoming MOT will pass with this nightmare...

[djh2]

It might be worth checking your earth locations for corrosion, there are a few located around the car.

[palmyra08]

Originally Posted by djh2

It might be worth checking your earth locations for corrosion, there are a few located around the car.

Thanks, I am trying to find some wiring diagrams, it is very puzzling how the "main" lights and radio stay unaffected, apparently some tail light grounding issues were seen on similar models but I am quite stumped where they may have hidden grounding points. I can just see a garage spending days "looking"

[djh2]

The xenon headlights have a ballast and do not run at 12v, so that makes sense to me that some intermittent noise may not show up that much.

The halogen lamps, LEDs etc would be susceptible. I am surprised that the radio is unaffected but I'm not familiar with the amplifier electronics.

[palmyra08]

Thanks, that makes sense then, indeed I was expecting some audio artefacts due to this (certainly from radio, but oddly CD player is also OK).

What I also cannot explain, none of the warning lights come up, so computer that is usually very sensitive in self-tests for bulbs etc., would not pick up on a very very floating ground? Bizarre... sometimes it flickers so much that is tragicomic.

There are some articles about tail light ground corrosion but so far could not find anything so visible like on the pictures posted here and there. Now where the ground points are for these circuits, is beyond me, could not find a single diagram on the net just some vague descriptions.

[Flyboy161]

I'd pick up a Bentley manual. Here are the earth locations, followed by their purpose.

[palmyra08]

super, many thanks, it gives me an idea, and wiggle some connections

[palmyra08]

A quick update, in the nice weather so far only dared to move an wiggle a bit the rear tail light connectors (which apparently can have some issues with grounding sometimes).
It may have been a co-incidence but flickering stopped 2 days, it came back today and this time the wiggling has no effect.
Oh the joy...

[doru]

On older BMW models, some similar electrical behavior (gremlins) were due to a failing ignition switch. But I believe you have the start/stop button. On the older cars, the symptom could be reproduced once the car was started, lower the sunvisor then turn on the sunvisor light by opening the mirror cover. Then the gremlins would start on a clockwork basis. And it was a relative cheap and easy fix. Yours might be different, but worth a try.
Keep us posted.

[palmyra08]

Indeed, start button... but certainly gremlins... e.g. footwell and radio lights do not flicker is not switching on parking lights, even with engine off as soon as parking lights turned on, the hell begins... starting engine makes no change to the overall look of how much and how often flickers. But everything starts the gremlins game except the xenons and radio audio or CD player is also unaffected, also the LED displays and dashboard instrument lighting doesn't flicker. Ridiculous...

[palmyra08]

Indeed, start button... but certainly gremlins... e.g. footwell and radio lights do not flicker if not switching on parking lights, even with engine off as soon as parking lights turned on, the hell begins... starting engine makes no change to the overall look of how much and how often flickers. But everything starts the gremlins game except the xenons and radio audio or CD player is also unaffected, also the LED displays and dashboard instrument lighting doesn't flicker. Ridiculous...

[palmyra08]

Quite stumped... checked the dreaded grounding wire problem in tail light connectors, not even corrosion, pristine contacts... ground points I could access inside car looked OK.
So this starts to look like a hugely expensive and possibly futile visit to some garage so they can replace half of the car "looking" for the electrical gremlins...

[palmyra08]

According to one garage, ground points would not explain the issue as all front and rear lights (except xenons) plus interior lights except roof (reading lamps) flicker "together" in unison as soon as parking lights turned on - the various lights use very different ground points, so apparently e.g. one corroded or floating one would not make everything go crazy.

Also because all windows, etc. all other electricals work perfectly and computer gives zero warnings in self-test about anything.

Suspected the switch, but... fog lights are controlled by two other switches, and those also flicker when parking lights turned on.

So booked it in, they do not even want to give estimate... this will either be trivial or mega-super-expensive after who knows how many days of looking?!

This surely must be a very dramatic simple root cause, I cannot imagine it being so rare...?

[Flyboy161]

Hmm...this is why I love and hate electrical troubleshooting so much.

[doru]

OP, I know that it doesn't make sense to have a failed switch that controls one thing to induce gremlins in a totally unrelated area. But check out this vid. If I were you, I would source a used switch from a wreckers yard and change it with yours. If nothing changes, than it might be some other switch/relay on the same bus. But take a look at the vid first and see unrelated gremlins popping from a failed ignition switch. This was documented multiple times early 2000's.

[palmyra08]

Many thanks, I was wondering whether the light switch plays up or something like that... garage so far, of course they cannot even guesstimate how long the may keep the car ... said that "switch may be sending current in wrong directions", which to me as former electronic engineer sounded a bit on the esoteric side ...
But it may well be that something makes contact where it shouldn't... it is weird that turning parking lights (engine not started) makes footwell lights also flicker, but not the reading lights on roof.
So found some electrical diagram site and keep trying to see any common pattern (grounds are very distributed and different in the different lighting that all flickers in perfect unison, so it brings me to tears ).

[sirdaft1]

Pull your FRM check for corrosion. I had moisture somehow get into the FRM and caused very odd electrical flickering issues. Swapped the FRM and everything works normal again. It's at least worth looking into.

[sirdaft1]

Pull your FRM to check for corrosion. I had moisture somehow get into the FRM and it caused some very odd/intermittent electrical flickering issues. I eventually swapped the FRM and everything worked normal again.

[palmyra08]

Many thanks everybody, apologies for no tangible updates from my end but the darn thing (again) completely stopped flickering since last night...
I booked it in for Monday so now let's see if it comes back, otherwise they can't diagnose anything...
I shall have a look over the weekend remaining things I can check, but maybe sunshine made it happier? I could so far find no weather correlation but who knows, moody E90...