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2003 chevy trailblazer_ltz
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24 Posts
Discussion Starter · #1 ·
Interior Lights Don't turn on When "Pushed". Only when switched on from Dash Knob.

Hi Guys!

I'm having an odd problem. You know those interior lights right above Each door on the side of the car? Well when you push on them, they are suppose to turn on. For some reason they do not. The only time I can get them to turn on is when the Car door opens at night, or if I turn the little knob to the left of the steering wheel all the way to the right until it clicks on (the knob that pops out when you push on it to control the dimness of the lights).

I also noticed that the Lights on my Sun visor mirror do not turn on no matter what I do.

Can anyone tell me what I can do to start checking these? I started checking fuses in the engine compartment (behind the battery) and under the rear drivers seat, but I still haven't found the one that controls that yet.

Any help would be appreciated.
 

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2004 gmc
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26,436 Posts
Good problem with a known fix. What's gone out for you is called the "inadvertent power" supply, and it's on a 20 minute timer run by the BCM to make sure that a pressed-on reading lamp or vanity light won't run down the battery. It's either fuse 4 (TBC 3) or fuse 40 (TBC 4) in the rear fuse block, or a fault in the BCM (that's more expensive).

I've told multiple members about these two fuses, but the shop manual schematic is not clear on which one actually runs the circuit in question. So if you find one blown, would you tell me which one so I can mark up my schematic? Thx!
 

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2003 chevy trailblazer_ltz
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24 Posts
Discussion Starter · #4 ·
OK I found a few things out:

The circuit you are refering to is number 40 (TBC4).

The number 4 fuse (TBC3) is just for the interior lights all together.


Here is the odd thing now...
When I replace the TBC4 fuse with another 10A fuse, it immediately blows. Even when the car is not on. The only time I can replace it is when I replace it with a 20A. That seems to work fine, and allows the lights to work as they should. Although I wasn't sure how safe it was to keep that fuse in there so I took it out. Anything I can do about this?

Also, the lights on the visor mirror still do not work.
 

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2007 chevy trailblazer_ls
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184 Posts
You have a short, and if the visor mirrors still do not work, I'd start there:m2:
 

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2007 chevy trailblazer_ls
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184 Posts
This may sound odd, but I've had bulbs short out that cause the fuse to blow, hasn't happened recently, but it has happened to me in the past. Start ther, then move to the visor's. If you can find the connection and unplug it and then replace the fuse, this may narrow things down.:m2:
 

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2009 chevy
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6,513 Posts
Your on the right track, just to clarify the circuit (in case you haven't taken the cover off any of the lamps), there is a courtesy lamp (on with doors) and a reading lamp (on with doors, if not on with push on cover).
One of the reading lamps might be bad, but it would also blow the other fuse when off.

The visor lamps do not have this "double on" feature, so they only operate from the fuse that is popping.

You might have a jammed wire (pinched) that is shorting to a high ground. That could explain the 20 holding.

It's the orange wire, going to the lamps, may need to meter it.
 

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2003slt

I read this yesterday. I haven't had been able to make my interior lights work in the map light mode (on when they are pushed) ever. I bought the truck new. I checked fot the blown fuses mentioned. The fuse was none existant. Evidently wasn't there from day one. Put in a 10A and voila, map lights and vanity lights work.

I do 95% of all maintenance and repairs myself. I just replaced the front left bearing/hub assembly last week. It was making serious whinining noise. Timkin for $200 at autozone. I wouldn't use any non-named brand made in China bearing.

103,000 miles, solid as the day I bought it. Plan to keep it for 147,000 more.

I truly appreciate all of the info I get from this sight, everyone keep up the good work.:hail::hail::hail::thx
 

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2005 chevy trailblazer_ls
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177 Posts
Just do not put a shunt in the block and wait for the smoke to expose its self. Although it may locate your fault , it is a PITA to put the smoke back in the wire.


did that on my first car back in the day . My shunt was a t20 staple :weird:
 
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