Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner
1 - 11 of 11 Posts

·
Registered
2002 gmc envoy_slt
Joined
·
32 Posts
Discussion Starter · #1 ·
Hey guys, here is my issue in a nutshell......

There are 4 cars in my house.....Honda, Acura, Ford, and Envoy....on the first 3 of them, both FM and AM work flawlessly, with great reception and no static, especially in the AM band.

On the 2002 Envoy, the AM band is very much subject to static and station bleed at times, but what really annoys me most is that each and every time I step on the brake, there is an additional whistle / hiss that comes thru the speakers (only happens when listening to AM radio). I have narrowed this down to having something to do with the brake lights, but I am at a loss as to how to proceed.

Any ideas ?. I'd like to fix both issues, but the brake light interference thing would be the most important....I can live with the rest.
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
5,268 Posts
im not sure about this answer...
but im tempted to say you may be getting interference from the 3rd brake light- (NEON tube)- since it uses some sort of ballast to power up that neon tube- and you say it happens when you step on the brakes.....
If I were in your shoes... I would test this out...
in the fuse box- there should be a fuse labeled something like CHMSL...
for center high mounted stop lamp... (or similar)...
remove the fuse so that the 3rd brake lamp stops working.
then check to see if you still get the noise when you press the brakes.

in your manual.... page 6-61 and 6-62

under your reat seat fuse box,
removed fuse # 16- labeled VEH CHMSL
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
No, it may be a bad antenna ground or broken coax going to the radio that should be rejecting the natural noise from the ballast. My wife's Honda had AM problems that were a broken wire internal to the antenna.
 

·
Registered
2002 gmc envoy_slt
Joined
·
32 Posts
Discussion Starter · #5 ·
Well, I just tried the fuse thing, and there was no noise when applying the brake, so there is definitely a relationship between the 3rd brake light and the whistle on the AM band. As soon as I put the fuse back in, the hiss came back. I agree that I may have an antenna problem in addition, due to the constant bad reception even when the brakes are not being used.

So......how do I go about tracking down an antenna problem ?.

I'll try the 3rd light thing as a last resort.

Thanks.
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
So......how do I go about tracking down an antenna problem ?.
Remove the coax from the back of the radio. Get a meter. Check continuity from the center of the coax to the antenna mast, and fromthe shield to the car chassis. Make sure the center of the coax isn't shorted to the shield. Buy a cheapie if you want to confirm the diagnosis before buying another GM one or one off Ebay.
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
5,268 Posts
No, it may be a bad antenna ground or broken coax going to the radio that should be rejecting the natural noise from the ballast. My wife's Honda had AM problems that were a broken wire internal to the antenna.
like he said- if the noise goes away- then the antenna is somehow picking up the noise

so we know that the antenna cable is not shielding against the noise.

Like he said- you can buy a cheapie antenna and plug it into the rear of the radio to see if the noise is still there.

You can also try an inline noise filter at the antenna... or try one of these...
at $2.99 it wouldnt hurt to try

http://www.radioshack.com/product/index.jsp?productId=3012599
 

·
Registered
2002 gmc envoy_slt
Joined
·
32 Posts
Discussion Starter · #8 ·
....Thanks, and now two more questions......(sorry I'm an idiot).


Instructions on accessing the back of the radio to get at the coax ?.


On the snap-on filter......where should I put it on the coax.......near the radio, or near the antenna ?..........I have the in-glass antenna in the back window.
 

·
Registered
2002 chevy trailblazer_ltz
Joined
·
5 Posts
Same story

Mine 2002 TB developed exactly the same brake-AM interference relationship. I have CD changer, ABS brakes. Sound system and brakes work flawlessly, EXCEPT that hiss/static like interference on AM bands only as soon as brake pedal is even slightly depressed. Almost like bad contact/ground somwhere in brake electrical circuitry. What "blue light" are you guys talking about ?. Help Rodie, Help!:(
How do I start this troubleshoot ?
 

·
Registered
Joined
·
28 Posts
The AM antenna is mounted internally in the radio. The one that is referred to on the back of the radio is the FM. An AM signal requires a long piece of wire to receive the signal. Much longer than an FM signal requires. 99% of all radios produced that have AM band available, have the antenna mounted strait to the circuit board. I can not remember off hand how long it has to be, but if you were to pull apart your radio, or any other radio, the antenna would be a bunch of wire wrapped around an iron bar.

To the recommendation on checking the brake light, great call. As for what to do about it... Might be cheapest to look for swapping to an LED brake light... I have never looked into such a task, but option 2 would be replacing the radio. I hate to admit it, but I think my 02 Envoy is full of noise that would interfere with any AM band signal. The electronics there are stuffed into a small space, the more your going to get signal noise.
 
1 - 11 of 11 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top