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Destroyer of Cones
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Discussion Starter · #1 ·
Background of Issue
Many of the early 2007 tC's have had issues with the HVAC lighting working intermittently or stopping all together. If your HVAC lighting only works sometimes, goes out when the headlights are turned on, etc, this is probably your issue. If the car is under warranty and the dealer is going to fix it, they simply replaced the HVAC unit. However, those that are out of warranty or have done an LED swap probably arent always so lucky. The remaining alternatives have been either buying a new HVAC (around $500) or purchasing a salvaged one ($50 - $100).

The Fix
I was finally able to get one of these sent to me that I could plug into a test harness and test. I spent some time mapping out more of the lighting control circuit (I had mapped a good amount of it previously during design of the LED mod for the HVAC, but not the input and dimmer control portion) and found the issue. I have since had one other person try this fix on theirs successfully as well, so while this may not be the only possible cause, chances are this is the one causing the common issue. The issue is a couple of cold solder joints on the legs of one device. The fix is detailed below.

1) Remove the HVAC. There are plenty of threads and DIY writeups on the forums detailing this part, so I wont add all of that here.

2) Remove the HVAC from the housing so you have the bare board.

3) Locate T302 on the front of the board right under the hazard button. This is a 3 legged device (a transistor) that controls part of the lighting function.

4) With a low power soldering iron with the tip tinned just a tad, reheat the solder joints on each of the three legs so the solder reflows.

5) While you are at it, go ahead and check T303 right next to it.

6) Plug it in and test. The lighting should now act as normal!

A pic is provided below for reference. If you have any questions on this or have the issue and this fix does not work for it, feel free to contact me on the forums regarding it. Going forward, I will check every 07 HVAC that I perform led mods on for this and resolder the device for good measure to prevent the issue from popping up.

[/QUOTE]
 

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Destroyer of Cones
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7,066 Posts
Discussion Starter · #2 ·
Bump to possibly get this stickied. I would like for others to see this and try it so we can verify that this is the common issue. If so, I will ask permission to edit the post with better details and pics.
 

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Premium Member
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A friend of mine just had this happen on his tC, and I don't think he's fixed it yet. I'll ask if I can take a look at his to confirm if this may be the issue.
 

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Destroyer of Cones
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Discussion Starter · #4 ·
Apparently this will not be stickied, so I am bumping so people will see it and hopefully be able to try the fix.
 

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Ironhead
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Oh hold your damn horses. Here's your sticky.
 

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Destroyer of Cones
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Discussion Starter · #6 ·
:p

Figured I would prod and poke till it was accomplished :D

Thanks man..
 

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Destroyer of Cones
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7,066 Posts
Discussion Starter · #7 ·
It sounds like someone has tried this fix on thier car and it worked as well. As sooon as I can verify this I will post up a pic and a bit more info for the fix.
 

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Destroyer of Cones
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Discussion Starter · #8 ·
Fix appears to be the one. Waiting for the thread to be unlocked so I can edit it with more info.
 

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Destroyer of Cones
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Discussion Starter · #9 ·
Thread updated! Thanks to iGod for getting the info copied over quickly. Hope this helps some that have the issue.
 

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awesome find Dave!
 

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BINGO! :bow:

Thanks for finding that... shortly after reading this post, I popped out the board, stuck it under my microscope (I have an electronics bench with a stereo microscope, hot air rework & temp controlled soldering station, oscilloscope, function generator, etc) and re-soldered it... and a few other components in the area that looked like they had been installed by blind monkeys! :shock: Popped it back in, went for a ride, and works like new! :naughty:
 

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First off I wanna thank engifineer a whole lot I did exactly what you said and its works perfect now!!!! also for the toyota scion dealers and service advisor go back to school or sit on #### because i went to toyota of orlando and told them the issue and they all told me they never heard of this issue. one tech said her work thier for 13 years and her never heard that also they told me the only way to fix it is to replace it WRONG im not going to pay (763.64) for that unit. they know how to milk us american tax payers for money when were struggling in this economy. anyways for all that have this issue with the 2007 scion tc also please follow the direction carefully that engifineer was so kindly to share and i promise it will work. for those who has the same year model as mine please also check your spoiler and the rubber seal around your windshiels and check to make sure your sunroof work properly thier was a recall for that issue also thank guyz and ladies
 

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I just wanted to thank the author for this post. My stepdaughters tC was experiencing the same problem and the directions did the trick. My one bit of input is that the component in need of soldering is very tiny. Magnification was a necessity for my 48 year old eyes (two pairs of reading glasses at the same time did the trick). Also, when I attempted to do the first leg, the component came instantly loose from the board. I guess the other two legs were not attached. After this minor setback, I used a regular pair of tweezers to hold it in place while I did the repair. If I had known better I would have held it in place the first time as it is hard to position such a small item when it is not connected at all. Anyway, I am far from an expert at these kind of things and was able to pull it off. It is very rewarding to save over five hundred dollars. My only expense was a nine dollar soldering iron (15 watt) from Radio Shack.
 

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LED Maniac
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i commend you for doing the work yourself. :thumbsup: :clap:
always a good feeling to get something broken working again. ^_^

a $9 fix? hell yea.
 

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Frequent Flyer
2007 Scion tC
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Wow thank u for reviving this thread. My HVAC lights have gone out on my 2007. Luckily it's still underwarrenty.
 

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Destroyer of Cones
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Discussion Starter · #17 ·
Yeah, it should be mentioned to hold the part down with the tweezers when you touch up the solder joints.. just in case the other two are both loose.

Glad it is still helping some people!
 

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Will this work on a 2008? I've got a lot of soldering experience and I'm having the same problem, I turn on the AC and extra stuff lights up partially on the display and changes when i raise and lower the fan. The dealers saying my warranty won't cover it because the previous owner did some work with the lighting under the speedometer.
 

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Destroyer of Cones
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Discussion Starter · #19 ·
Doesnt sound like the same issue at all unfortunately, so I dont see this being the issue. Also havent heard of that issue on an 08.

Is the lighting color on the HVAC anything but orange? If so, whomever changed it out may have caused some solder bridging on the LCD pins.
 

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THANK YOU!!! Great instructions. My '07 tC's HVAC lights stopped operating when I turned the headlights on, like other posters. And wouldn't you know it, the car was four months past the three year warranty. I'm neither a car person, nor an electrical engineer, but even I was able to make the repairs with your guide. You saved me hundreds of dollars, so let me know if you're ever in Boston and I'll buy you a drink. Thanks again!

Note to other fixers - it took me a while to track down good instructions for taking apart the center console. You might find these links helpful:

How and where to pull the plastic housing off the center console, and remove HVAC unit (starts on p. 6). Great photos.
http://stores.mengmotorsports.com/images/M...moval+Guide.pdf

Step-by-step instructions for how to remove the HVAC PCB from the unit.
NOTE - author forgets to mention that you must remove the nut and washer that go around the HVAC control knob shaft in order to get it off the plastic housing plate - removing the screws is not enough. It's on loosely, so just use a pair of needle nose pliers.
http://scionlife.com/forums/showthread.php?t=14143
 
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