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Old 05-24-2016, 01:19 PM   #1
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Issue with pulsing DRL LEDs.... SOLVED!!! Focus S/SE/Ti 2012-2013

If you are having issues with the newly installed LED DRLs pulsing when you turn on both your ignition and headlamps, do not fear!

The issue stems from the cheap relay control module the DRLs come with. They were not designed appropriately for modern cars. Modern cars have what is called a TIPM that serves as a central location for controlling all the electrical systems. The TIPM powers the headlights with a PWM voltage (squarewave) rather than a constant 12V/14V DC. Newer cars utilize this method because it prolongs the life of the incandescent bulbs and uses less power.

So the flickering we are seeing is a result of the headlights being turned on and off at about a 110Hz frequency (thats what I observed on mine). Because LEDs have a significantly faster on/off response time than an incandescent bulb we can see the LEDs react to the PWM signal while the headlights remain steady.

OK, so how to fix it? Pretty easy actually if you have the right tools and the patience to open up that damn hood one more time. You need to build a low-pass filter that will filter out the ~110Hz squarewave and leave you with a "flat" DC signal to trigger your DRLs.

You will need a 2.2k ohm resistor, 4.7uF capacitor, soldering iron, and some wire or prototype board. You can use a ceramic capacitor or polarized capacitor, it does not matter. However, make sure if it is a polarized capacitor to wire it up correctly with negative lead to ground!!! Also, 4.7uF is about as high as you want to go. I experimented with a few different values and going too much above 4.7u overloads the headlight circuit. Here is a picture of the circuit:

Here is a picture of the low-pass filter connected up and DRLs running 50% with engine and headlights on.

Hope this helps some of you out there experiencing this annoying issue.

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Old 05-24-2016, 03:09 PM   #2
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