LED light bulbs not recognized on cars equipped with CAN bus?
Here is my story how you can make them light up for a few cents.
The day had come when the board computer informed "parking light right broken" or something like this. I removed the light bulb and found this type:
To my surprise the local chinese shop didn't have any of these old style bulbs, but only white light super fancy LED bulbs. Two for two $, well, I could afford it, 15 000 hours of life time, so they would live longer than myself and the car together :-)
I happily fitted one still at the parking and found it not working, the board computer still complaining about a broken bulb. Back home I connected the culprit to my power supply and it worked fine, 20mA power consumption, and nice white light.
So, what happens here: the CAN bus of the car monitors these light bulbs, and if one doesn't draw current, then the assumption is that it is defective.
The LED draws current, but so little the CAN bus thinks there is something wrong, AND disconnects the 12V power from that bulb too. I gave up for that evening.
The next day I've spent many hours of research on the internet and found only "solutions" where people connect 5W power resistors in parallel to their LED lights. Anyone with an electronics background knows how hot 5W on a small surface of a resistor get, and for the others, be assured that this is VERY hot. Just touch an incandescent light bulb and you will get an idea, you ll not do it twice.
It seems nobody had tested what the smallest resistor would be to trick the CAN bus to deliver power to the LED light. So I started my tests. A 1200 Ohm resistor did not do, the light turned on for one second, then off for 3, and on again. So I put a 380 Ohm in parallel, this was enough for the CAN bus, and the light stayed on, with no warning of the board computer.
However the 380 Ohm resistor got quite hot, so I replaced it by a 680 Ohm. This one did not get too hot, the whole bulb drew 40mA, and me and the CAN bus were satisfied.
Just make sure to give some space between the resistor and the LEDs of your bulb, the LEDs dont like heat at all.
I hope this gives an idea to others how to "tune" cheap light bulbs in newer cars. Bear in mind, that such an LED bulb has a + and a - or scientificly an Anode and a Cathode. Therefore you need to measure first which wire of the old bulb has plus or minus. Mostly the brown wire is the minus or the ground of the car chassis.
Let me know if this helped and if you have any questions, please post a comment.
