How to modify the tail lights failure sensor for UCF20/21 - Club Lexus Forums


How to modify the tail lights failure sensor for UCF20/21

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Old 06-26-14, 04:58 AM   #1
Yamae
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Default How to modify the tail lights failure sensor for UCF20/21

To those who are trying to find the way to stop the “tail lights failure light” for models after July 97. For UCF20/21 before July 97, see post #8.

Below is the way to disable the module. All you need is just to lift up or remove the resistor indicated by yellow letters “Lifted”. When you use LED tail lights, this is simple, easy and safe compared to use high wattage resistors that generates more than 150 watts of heat.

So far I have asked this by several people and I decided to open this here.
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How to modify the tail lights failure sensor for UCF20/21-modding-ucf20-21-current-sensor.jpeg  

Last edited by RA40; 07-01-14 at 12:01 PM. Reason: to add UCF20/21 before July 97, see post #8.
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Old 06-26-14, 09:00 AM   #2
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Thank you for posting this!

It should definitely be added to the FAQ section....
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Old 06-26-14, 09:36 AM   #3
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ahh..these types of posts and info is what we look for from you yamae,awesome
maybe retitle it and have LED in there somewhere
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Old 06-27-14, 11:27 AM   #4
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Since my trunk liners were all removed anyway I tried this fix last night and worked like a charm!

Literally done in 2 mins from start to end. It is that easy once you have the liners removed...

Thank you again Yamae san!
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Old 06-30-14, 02:25 PM   #5
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where is the module located? great work yamae! thank you thank you thank you!

is that it in the red?
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Old 06-30-14, 05:37 PM   #6
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Quote:
Originally Posted by timmy0tool View Post
where is the module located? great work yamae! thank you thank you thank you!
The one at the left indicated by a yellow asterisk.
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Old 06-30-14, 08:21 PM   #7
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Is there a how to for this for 95 and 96 models?
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Old 06-30-14, 11:51 PM   #8
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Quote:
Originally Posted by Caniac14 View Post
Is there a how to for this for 95 and 96 models?
Here it goes. Lift or cut the leg of the resistor indicated by X.
Now I think I'd better change the title, but I can't do that. Will a moderator or someone, please change it. May be "How to modify the tail lights failure sensor for UCF20/21" would be better.
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How to modify the tail lights failure sensor for UCF20/21-ucf20-early-model-failuer-sensor.jpg  

Last edited by Yamae; 07-01-14 at 12:02 AM. Reason: To request to change the title.
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Old 07-01-14, 10:14 AM   #9
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Ok cool. Is this in the same little red box posted a few replies earlier?
And is the box easy to open, do I need to take care opening it?

Last edited by Caniac14; 07-01-14 at 12:11 PM.
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Old 07-01-14, 12:06 PM   #10
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Thanks Yamae
Title changed. A definite addition to the FAQ.
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Old 07-01-14, 08:32 PM   #11
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Quote:
Originally Posted by Caniac14 View Post
Ok cool. Is this in the same little red box posted a few replies earlier?
And is the box easy to open, do I need to take care opening it?
Oh, Yes, for both. But you need to remove the trunk liner some though.

Quote:
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Thanks Yamae
Title changed. A definite addition to the FAQ.
Thanks for the change, Mike.

I only have introduced the way to disable the function to detect the open tail light or the reduced current.

There is also a way to modify without disabling the function. This can be achieved changing the current sensing resistors shown in the photo at my first post. There are 3 sensing resistors which generate the minor voltage drop. The voltage drops are monitored by window comparators and when the voltage is out of the range, the error signal is generated.

Changing those resistors can keep the function on, but you need to do some experiments. Depending on reduced currents, you have to use matched resistors. Some LED tail lights consume the energy 1/5th and some 1/20th like mine which has high efficiency LEDs for industrial use. Depending on the reduced current, you need to select and use matched resistors.
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Old 07-02-14, 12:24 PM   #12
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sounds good yamae!

i would like to keep the function but you're right, it will take some current and load measurements to find the right resistance. my LED bulbs cause static on my radio when applying the brakes so i know they have a different load rating than the average units.

also the comparators may have a small window to sense the voltage drops. i was thinking of putting a potentiometer (adjustable resistor) and adjusting until the load is just right.
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Old 07-02-14, 12:43 PM   #13
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Good post. Thanks to all who make it happen.
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Old 08-05-14, 06:26 PM   #14
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Quote:
Originally Posted by Yamae View Post
Here it goes. Lift or cut the leg of the resistor indicated by X.
Now I think I'd better change the title, but I can't do that. Will a moderator or someone, please change it. May be "How to modify the tail lights failure sensor for UCF20/21" would be better.
I did this and my tail-light out thing still comes up my dash.
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Old 08-06-14, 11:32 AM   #15
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Quote:
Originally Posted by Caniac14 View Post
I did this and my tail-light out thing still comes up my dash.
what LED tails are you using?
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