CAN Bus is a multiplexed wiring system used to connect intelligent devices such as Electronic Control Units (ECU's) on vehicles, allowing data to be transferred in a low-cost and reliable manner. CAN means 'Controller Area Network' and was developed by Bosch in 1980. Most new vehicles use this system and it is becoming increasingly difficult to install after-market products without using a CAN Bus Interface.
This days it is a standard in cars such as BMW, Mercedes, Audi etc manufactured after 2005 or 2006 year. For sure it was used in higher class models, but not sure about middle range cars.
Now, this days it is very popular changing standard side bulbs such W5W 501 for LED ones.
LED side bulbs can cost between 4 and 20pounds, it all depends from where you getting them from and how many LEDs have each bulb and they structure- build-in extra resistors etc.
LED bulbs offer a much longer lifetime and very bright and clear light, either crystal white, white with a bit of blue, completely blue or even they can change color from blue to red and green etc.
BUT, they also use much less energy than for example standard W5W 501 side bulb or even H11 LED fog light, and thats where the problem is with modern CAN-Bus wiring system.
Why???
As CAN-Bus is sort of 'intelligent' wiring it monitors lots of other features and one of them is the wattage / working state of light bulbs.
When light bulbs burns out, consumption of electricity goes down to zero (this is base on Audi's A8 system) and automatically system bring NO BULB warning. Usual it also displays where is the faulty bulb and indicates it by flashing or lighting red color.
So because one of the main feature of LED light is a very low wattage/consumption, as soon you plug in the LED bulb, CAN-Bus records a lower consumption than a standard bulb (originally programmed in the system) and therefore brings the NO BULB ERROR as it thinks that bulb is burned, not so intelligent on the end of the day
This days, you can buy an ordinary LED replacement bulbs such as fog lights or side bulbs or number plate bulbs etc, or the CAN-Bus compatible ones.
But, it does not always do what it says on the tin.
Very often you will need to connect them together with a resistor or get the ones with resistors already built-in.
This is base on my recent experience with LED side bulbs on Audi A8 (D3 4E).
On the beginning I went for the expensive ones as I thought thats the way to do it if you want to get it right as choice is massive this days.
1st set I bought from Auto Bulbs Direct - 16.99 for pair / 2LEDs per bulb / CAN-Bus version
http://www.autobulbsdirect.co.uk/501...b_search=c1100
RESULT - NO BULB error, not good, very disappointing.
2nd set I got from another online retailer - 9.99 for pair plus postage / same design 2LEDs per bulb, but with different resistors built-in
Thats how they looked, by the way they should be crystal white and they were blue
RESULT - NO BULB error, well again very disappointing
3rd set I got from a very old good friend eBay which can be either a very good place to get certain stuff or the last place to buy
11.99 per pair, this time 3LEDs per bulb.
RESULT - NO BULB ERROR !!!!!!!!!!!!!!!!!
Just to check that there is no issue with the wiring, I unplugged the LED bulb and put the standard one, and error was gone straight away.
4th set I got again from ebay, this time I went for more LEDs per bulb to maybe increase the consumption which could finally be compatible with CAN-Bus, 7.99 per pair, 5LEDs per bulb
http://www.ebay.co.uk/itm/1706848328...#ht_2574wt_905
RESULT - well......as soon I switched the ignition on, system checked all other stuff and straight after that it came up with.........NO BULB error....BUT, both bulbs flashed red on the screen and after 15-20sec error was gone and everything came back to normal.
So I switched the ignition off and start the engine this time, ERROR came up, it beeped twice and it was gone in much less time the on the first attempt.
I haven't tried the 3rd time as I was in a rush, but it looks like system is getting familiar with them and in some sort of strange way (it is intelligent as they say) and its all OK after few seconds.
I will try it tomorrow few times and see what happens.
But if 2beeps and error message for just 10-ish seconds is the only issue, I may even leave them until I will know that there is something 100% tested and in full working order on my car as they look really really nice:
and together with the Osram Night Breakers Plus
and just to compare the standard bulb
If you have a car manufactured before 2005 or no CAN-Bus wiring, then you are good in getting any LED bulbs you want for your car.
I hope I didn't bored you to death
Also, I am not saying that you will experience same issue, it could be just issue with high class models or just with A8s, no idea, so don't get negative about it as you always can return bulbs within 7days at least, so it's always worth trying.
LED side lights / bulbs vs. CAN-Bus wiring system. 
Re: LED side lights / bulbs vs. CAN-Bus wiring system. 
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