Article by: Nybbles2Bytes
Article applies to: all BMW e36 models.
There are DIY’s out there showing how to disable this module when you put LED’s on however there is nothing to show how to make the module work completely correctly with LED’s–well, when I was looking about 2 years ago, I haven’t checked recently. So, I dusted off my electronics background from a very long time ago to see if I could figure this out and I did.
Caution: Check the pictures very carefully and make sure your module is EXACTLY the one I modified because if the wiring on the board or the components are different it probably will not work.
There are two reasons why the module gives an error with LED’s. Those are:
The current draw (amps) from LED’s is below the lower limit of the module’s “good range”.
LED’s take a little time to start drawing current whereas the module checks for a current draw almost immediately. The delay with the LED’s is because the LED’s have an electronic circuit that needs to power up before drawing significant current whereas the factory bulb is just an in-line resistor that shines so has no delay on drawing current.
To solve this we as need to do two things:
- Make the module work within the LED’s current draw.
- Make the module wait a little while before checking for a current draw.
To do this you can modify the module as follows:
Making the Current Range Correct –
First you need to know the difference in the current draw between your LED’s and the factory lights so measure both with a current meter and then calculate the ratio. For example if the factory lights draw 5.2 amps and the LED’s draw 0.65 amps then the ratio is 0.65 / 5.2 = 0.125:1 (1/8th).
Now look at the image below. You can see that I cut down two very low ohm resistors used for measuring the current via a voltage drop across the resistance. Just cut these down by the ratio you calculated so 1/8th the original height by our theoretical above.
WARNING: The numbers I used are just for example. YOU MUST do your own measurements and calculation to get this correct, do not use my example values above, it will almost certainly fail.
If you are so inclined to be more cautious then the way I mentioned above then you can do the following additional step–which I did and it gives you wiggle room to correct errors so it’s certainly wise.
After calculating the ratio, e.g. the 1/8th we used above as an example you can also, while having the factory lights attached measure the voltage drop across the resistors (put a volt meter lead at each end of the resistors) you see cut down in the image. Now, when you first cut down the resistor height (which makes the resistance higher) don’t cut it all the way. Just go some of the way, say about 2/3rds of what you calculated. Then attach the LED’s and measure the voltage drop across the resistors. From there you can see how close you got and “shave off” height bit by bit until you to get to be very close to what the voltage drop was with the factory bulbs.
Putting a Delay on the Module So It Doesn’t Look for Current Too Soon
Have a look at the images below. They show two things:
Where to cut the track on the back of the board, and;
Where to solder the resistor and capacitor on the top of the board.
Note: Resistors can go either way however capacitors of the type shown have a polarity so you must put them in one way only. The way in the pictures is the correct way–note the minus sign down the right side of the capacitor in the images.
Caution: Overheating electronics can damage them so only apply heat and solder for the minimum amount of time necessary to get a good joint.
Tip: You will have to scrape the coating off the chips/i.c.’s legs before soldering onto them.
The resistor is 10kΩ, the capacitor is 4.7µF which gives a delay of about 5ms to get to ≈60% of ≈12V and we can just call this an approximately 5 millisecond delay before it checks for current which in computer time is plenty.
And that’s it, you can put it back, put on your LED’s and the module should work perfectly with your LED lights if you did it all correctly.
The most difficult part–a helpful tip: For me the hardest part was measuring the voltage drop across the resistors of the module. This is because of where it is mounted in the car, under the driver’s side of the dash up in an awkward place to get to. My solution was to both pull out the driver’s seat and plug the board in without it’s case and have it hanging down where it was accessible.
The one issue I had was that when I changed my LED lights I had to redo the shaving of the height of the resistors because between the two purchases they became more efficient so the second purchase drew considerably less current. I suspect they have settled down in efficiency by now so hopefully that will no longer be an issue.
Disclaimer: Obviously do this at your own risk, I’m not going to guarantee this will work for you, I’m just a DIY’er like you. However, I have been running my LED headlights for about 2 years now like this without an issue except one of my headlights on my first set of LED headlights did fail and the module told me as soon as it happened just like it’s supposed to so it’s already proven it’s worth to me.