Technical brake light woes

[Big Black Stilo]

about 2/3 weeks ago my passenger side brakelight blew, car told me this and indeed wasnt working.

i took out the bulb which was blown, so i replaced it all. No problems there then.

then, about wednesday this week, i had to emergancy stop. on doing so the bulb failure message came up for the passenger side. But during the drive hime it was flickering on/off and really getting on my tits.

I got someone to stand behind the car while i activated the lights, and it wasnt working. Then the message went and it was working, so checked for loose connections, bulb condition, type, etc and all is fine. i even popped a new bulb in as well

The rest of this week i have had intermittant bulb faults from that side on the brake light, and a work mate who followed me said sometimes it was working, sometimes it wasnt.

This is confusing the hell out me now as its only effecting one side. How does the bulb warning system work and how is it earthed to the car?

 

[Argonought]

As you suggest, most likely a bad connection/earth somewhere in that area.

I'd remove BOTH light clusters if I was you and carefully check for any connection issues - can be useful to transpose bulbs too.

 

[Big Black Stilo]

im thinking it maybe an earth issue.

how does the car pick up a bulb fault anyway? i noticed it does it without the lights actually being switched on.

and although this maybe sill but is the cluster earthed through the three connection bolts that hold the cluster to the car?

 

[Big Black Stilo]

nobody know how the car detects a bulb fault?

 

[Argonought]

There are only two ways - resistance checks of the filament or an optoelectronic sensor. The latter is foolproof, as it measures photons, but is liable to go faulty itself.

The Stilo almost certainly measures circuit resistance to check for faulty bulbs which means, using low voltage, it can detect a faulty bulb without actually illuminating the bulb itself. It's likely to be based on a variation of the Wheatstone Bridge principal.

It will detect open filament faults (the most common bulb failure by far) very effectively but I suspect it may be fooled by shorted filament faults.

 

[Deckchair5]

Yes, check carried out on resistance/ return voltage -if the resistance isn't right then it will fire up a failure even if the bulb itself it fine. Best to imagine it's saying "Brake light circuit failure"

 

[Big Black Stilo]

ok, so i've checked in situe and indeed, it is not working.

so i dismantled it and yet again the bulb is fine. i swap bulbs over from the other side, test it for 5 or so minutes, no problem.

re assemble, get 5 minutes down the road and beep beep beep stop lamp failure on the passenger side, again, and the light is not coming on.

no damage on the cluster board and the bulb in that side now is the fiat original, and that bulb isnt blown

 

[Deckchair5]

I had a poor contact on mine where the connector attaches to the light cluster circuit board giving the same warnings as you have. A clean up there with a normal pencil eraser or contact cleaner and some very careful moving out of the connector pins to make a better contact and have never had a warning since.

 

[Big Black Stilo]

cheers decks, i'll have a crack when i find my needle-nose pliers

 

[Big Black Stilo]

ok, i have made sure the connectors are not pushed down and away from the bulb- again, worked for 5 minutes then beep beep beep

so cleaned up the contacts and again, beep beep beep.

the only thing now is it is flicking up the fault every couple of minutes so all im getting is beep beep beep every 2 mins, which is annoying.

 

[Stuart_89]

my stupid passenger side brake light is doing the same, does it for a few days then works fine for a day then the god dman beeping begins all over, i was guna buy a new bulb, but what about the connectors you are on about, what are these and where are they and what should i clean them with?

 

[Big Black Stilo]

the connectors are the pieces of metal at the bottom of the bulb carrier on the cluster.

im starting to think my wiriing got damaged when i changed the bulb

 

[Deckchair5]

I'd make sure you've got a good earth at the cluster. Jam something on the brake pedal and turn ignition on, now put indicator on for that side. Watch the brake light and see if it dims in time with the indicator. If it does, do a voltage drop test between the bulb earth and good earth point at the rear. Again anything over the magic 0.2v and there's your problem

 

[Big Black Stilo]

no drop in the brake light when indicator on

 

[Deckchair5]

This is a 3 door isn't it?
Just have to be systematic about it. The fact the brake light actually does go out means an open circuit provided the bulb is still intact and the car is warning you the resistance isn't right

Never ignore the obvious, a poor contact at the bulb itself will cause all these problems. Lightly score/clean the surfaces and make sure the spring in the contact is enough to contact the bulb with enough force

It's extremely likely to be at the cluster circuit board but I would also check for near zero resistance between


connector E22 on the body computer and the cluster connector pin 4

the cluster connector pin 8 (black wire) and a good earth on the car body

 

[Big Black Stilo]

cheers decks, TBH im just going to get shut of it as i think its about to turn into a money pit