Had to remove the LED brake lights - interferred with the HID fogs - The Unofficial BMW M5 Messageboard (m5board.com)

MAH · 3rd December 2001, 00:44

All,

I have had to remove my LED brake lights(all 5 of them) because they were interferring with my stage II HID foglights. I realize that this may sound strange, but this was the case.

When I added the new foglights(they are great) they would go out when I applied the brake at idle. I did everything I could think of to make the problem go away. Mostly different connections posative and negative in the engine area. Nothing worked. HIDs4less could not understand the problem either.

I finally took out the LED's and that solved the problem. It makes no sence because the LED's draw only a fraction of the current that the normal brake lights use. In fact, I added an extra set of brake lights to the unused area of the lense. Even with 5 regular brake lights working (instead of the normal 3)I do not have the foglight problem any more.

Anyone have a clue as to what the problem may have been?

Mark

greg · 3rd December 2001, 00:58

Very weird indeed. All I can come up with after a few seconds of thought is that the instantaneous nature of the LED's (as opposed to the current itself) is creating a little voltage downspike that is confusing the HID power supplies.

If this were the case, you could soften the spike to the HID supplies with a good size capacitor across the 12V power to the HID supplies. The capacitor acts like a battery - when you apply power it charges up (very fast - in fact you may want to include a current limiting resistor in series with it, although I'm not sure this is necc. ). When the "dip" happens, the capacitor would discharge to make up for the lower voltage - pulling up the voltage close to the HID supply.

Just a hunch.

rvacha · 3rd December 2001, 03:47

Very strange! While LEDs light up instantaneously, they should be more friendly to the system than the old incandescents. As has been mentioned, LEDs draw just a fraction of the current of incandscents. Incandescents are tough in another way - initial turn-on surge currents are very high. The reason for this is that tungsten has very low resistance when cold. When the lamp is turned on, the low resistance results in very high current flow. As the filament warms up, the resistance goes way up and the current drops. As a rule of thumb, incandescent surge currents (usually called inrush current) are 10 times higher than the steady state current.

So.... what else can be going on? I'm not sure, but could there be more electronics in the taillight assemblies than just the LEDs and some resistors? Can you see anything inside the assembly? Have you ever asked your dealer if one of the car's modules has to be re-programmed when LEDs are used? Do you ever get a "Check Rear Lights" message in the MID?

Good luck and I hope you can get them back on some day

atomic80 · 3rd December 2001, 04:00

Mark:

That's really too bad..I was looking forward to trying the LED lights in my brakes. At least your foglight problems were solved.

Jason

Loz · 3rd December 2001, 15:50

Hi
In another thread I've been asking how do you remove and replace the Fog lights. Can you help, please.

Loz

MAH · 3rd December 2001, 17:56

Guys,

Thanks for the feedback.

Greg - Good idea with the capacitor. There is a relay in line because the exsisting wiring harness for the foglights was not large enough to take the current draw for the new power supplies. I will try your idea with the LED's back in.

racha - I did receive a "check brake lights" message when I installed the LED's. I thought about putting some additional resistance across the LED's. Thanks for the insight on the start up qualities of LED's. I will try Greg's suggestion. There is nothing else in the rear taillight assembly except the bulbs. What else should I try to get rid of the stop light message?

Jason - I am sure I will be able to work these small problems out. This is always the problem when you are modifing an exsisting system. The fogs are great!

Loz - The fog lights are very easy to remove. There is only one screw holding them in. You have to yank the plastic molding off around the fogs first. Don't worry, it does snap off without breaking anything. The one screw that holds them on is not a screw, it is a nut. Use a nut drivier to remove this. DO NOT mess with the adjustment screw that is a cross tip screw. The bulbs take a half turn to come out of the base. Do not touch the bulbs with your skin. This is an easy process. Hope this helps.

Thanks,

Mark

Loz · 3rd December 2001, 19:14

Thanks a lot for the help MAH
Much appreciated. I've ordered the part and it should be here in a couple of days.

Loz

dwasifar · 3rd December 2001, 20:52

Another thing you might try is using an electronic buffer relay to isolate the LEDs from the original taillight circuit. Give them their own power feed and use the relay to trigger them.

rvacha · 4th December 2001, 06:43

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!

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