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Ross
07-09-2008, 02:46 PM
I know it belongs in the 3 forum but all the action is here so please forgive me.

The check control on an '88 325 displays the brake lights warning even though all the brake lights are working and have the correct 21w bulbs.
The high stop light also functions and has the correct 5w lamp. I've exchanged bulbs anyway, again with the correct ones but to no avail.
Since the brake lights work the switch is good so what else?
Anyone seen this before and know the cure?
Thanks
Bill R.
07-09-2008, 02:50 PM
sockets for all the bulbs... corrosion on the socket changes the resistance value and even though the lights work the check control detects it as a fault.




I know it belongs in the 3 forum but all the action is here so please forgive me.

The check control on an '88 325 displays the brake lights warning even though all the brake lights are working and have the correct 21w bulbs.
The high stop light also functions and has the correct 5w lamp. I've exchanged bulbs anyway, again with the correct ones but to no avail.
Since the brake lights work the switch is good so what else?
Anyone seen this before and know the cure?
Thanks
Ross
07-09-2008, 03:59 PM
I'll have another look at the sockets. I gave them a glance and they looked okay.
Is there another common corrosion point?
Mr._Graybeard
07-09-2008, 10:35 PM
A faulty brake light switch is a common source of this problem.
Ross
07-10-2008, 02:15 PM
No corrosion in the sockets but I scuffed them up anyway, no joy. The connectors look good as well. Sigh
bubba966
07-10-2008, 06:32 PM
No corrosion in the sockets but I scuffed them up anyway, no joy. The connectors look good as well. Sigh

Which brand of bulbs are you using? Cheap bulbs use metal/metals in the base that are cheaper and don't conduct electricity very well which can cause the car to think the bulb is burned out and give you that brake light warning. Had that happen once when I first got my M-Sport. And it acted just like yours is doing now.

Also had the brake light switch go out on me. When that went out the brake lights didn't work at all. Luckily it went out in the parking lot of a BMW only repair shop that was able to sell me a new switch right on the spot so I could fix it then and there.
yaofeng
07-10-2008, 07:54 PM
Even my 540 has the occasional brake light failure warning on the check control, with no rhyme or reason. I'd like to know the solution to that too.
Ross
07-10-2008, 09:11 PM
I'm thinking perhaps NEW bulbs might be the answer. The ones I've been using are the correct Osram bulbs but used from the legions of old BMs that have passed through here.
Maybe a filament has broken and refused itself, I don't know, I've used half a dozen different combinations. Something is playing with the impedance on that circiut or the check control has gone 'round the bend. This car doesn't have any corrosion problems so it's a bit of a mystery.
If the new bulbs don't fix it then I'm not going to pull my hair out looking for some loose connection somewhere. I was hoping for someone to have had the same trouble and found an easy solution. It's 20 years old, I'll consider this to be "character".
kev535i
07-11-2008, 03:28 AM
had the same problem on my ol 325i and it was the switch- on the pedal - worked fine but resistance /impeadance values are very fine and it would trigger the warning - replace it they dont cost much
Ross
07-11-2008, 06:18 AM
had the same problem on my ol 325i and it was the switch- on the pedal - worked fine but resistance /impeadance values are very fine and it would trigger the warning - replace it they dont cost much
I hadn't thought of resistance in the switch, only if it makes and breaks the connection.
Certainly worth a look, thanks for the tip.
winfred
07-11-2008, 08:19 AM
the light control is probably dead, it's up where the amp hides on the left side of the trunk with 2 plugs, a 6 wire and a 8 wire
Ross
07-11-2008, 10:55 AM
the light control is probably dead, it's up where the amp hides on the left side of the trunk with 2 plugs, a 6 wire and a 8 wire
Thanks, I'll have a look there for corroded connections also. If the LKM is gone and isn't interchangeable with something on hand I'll just live with it.
I haven't tried a different switch yet but I suspect it isn't part of the circuit being monitored anyway.