The Unofficial BMW M5 Messageboard (m5board.com) - View Single Post - Had to remove the LED brake lights

MAH · 6th December 2001, 01:33

Quote:

Originally posted by rvacha
Hi Mark-
Lamps are tested periodically by the module by pulsing them very quickly and determining the resistance of the lamp. If the resistance measurement falls out of a certain range, the filament is considered bad and the Check Light message is displayed. My aging MY97 540 routinely reports light problems even though none are burned out - but I can be assured that one is going to fail in a few weeks (I've got one failing as I write this!)

The problem is that LEDs do not present the same resistance curves as incandescents and will fool the module into thinking there is a problem. BMW's E39 light module has supported LEDs since the initial launch of the vehicle - I have had my 540 reprogrammed by the dealer to accept a deck spoiler with integrated LED 3rd brake light. The reprogramming instructs the module to use a different algorithm to determine if the LED light is good or bad.

I suspect that the module has a built-in protection feature (electronic circuit breaker) that is tripping because of misinterpretation of the LED resistance curves.

Ask your dealer to reprogram the lamps for LEDs and see what happens. It is done via the DIS and there is a specific piece of software that is loaded. If you need the part number for the software, I may be able to find it somewhere

Good Luck!

Great information. Unfortunately, I still have the issue with the fog lights, but I am exploring the fix there. Interesing how you have a need to reprogram for the lights. I get a check front foglights message because I changed them to stage II HID's. Because the message says check front foglights, I am assuming the rear foglights are available overseas. Any of you UK guys have the rear fogs?

Thaks,

Mark