Faulty sensor on my rear lights...

[Andi38]

Hi guys..
My 1998 5 series is telling me a have a rear light not working on the dashboard and yet all my lights work. I looked at manuals, Internet etc but with no avail..
Can anyone help?
Where is the sensor in the taillight assembly? If I knew that I might know where to start...
Thanks :-)

[Stealthee]

You didn't happen to install LED bulbs did you?

If so then that is your problem and you likely need to install resistors.

[Andi38]

No it just came on, on its own.. I haven't changed anything in my lights at all..

[Blue Bowtie]

Originally Posted by Andi38

Where is the sensor in the taillight assembly? If I knew that I might know where to start...
Thanks :-)

The sensor is not in the lamp assembly. The BCM system monitors lamp current flow through shunts. If lamp current is below a threshold when lamp circuit voltage is present, the warning will appear.

As Steathee brought up, LEDs draw very little current, and changing to LEDs without adding some parasitic load to "fool" the system would generate the warning.

[Blue Bowtie]

The Cadillac system from 50 years ago (yes, 1967- 50 years) was far more effective. It used fiber optics to monitor actual lamp output instead of electrical load, and reported that to the driver. In another 20-30 years, perhaps the vaunted German engineering will catch up to old Detroit, err, Flint.

In the interim, check ALL the rear lamps, including the dual license lamps, side markers, etc.

[Andi38]

Ok thanks for that... Looks like I'm stuck with a faulty warning light permanently then...
It's wouldn't bother me as much apart from the fact it goes "ding!" Everybody time I start the car...