Trailblazer databus problem

I installed a viper 791xv on a 2002 Trailblazer. I used a 457gw for the locks and the passlock interface. Also have a metra GMOS-01 for the radio. It worked fine for 6 months until the trailblazer went to the dealership. They programmed the PCM. After they did the car would not start. They had the replace the PCM the get it to start. Now the locks will not work. I read a tech bulletin about removing the radio fuse if you have an onstar interface installed because it would fry the PCM. Well this is what happened but the car runs fine know. I replaced the 457g 2 times. I also replaced the GMOS-01.Still the 457g will not program. The dealership also reprogrammed the BCM and the PCM but nothing will work. Has anybody had this happen or know what could be causing the 457w not to program?

Any chance they cut away some of the connections from the installation? Mechanics seem to have a habit of doing that.

No I checked that. I have recheck every connection on the 457g. It just will not program. The light stays on solid.

are you sure its seing ignition becuse the light is suppose to flash when you turn the ignition on the you relesase the button to start the truck so it can learn the passlock like chris said double check youre connections sometime its just a small detail a loose groun blown fuse something small

I checked the wires again with a voltmeter. Its getting 12v on ignition but it will not read the data signal.

did you use a logic probe to verify that there is actually data there?   could be they cut the data wire somewhere before the OBD connector....      just a thought......

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Kevin Gerry
Certified Electronics Technician
MECP First Class Installer

Owner/Installer
Classic Car Audio
since 1979

I will try that but I read a OBD code off the other day so I think the data wire is ok. We'll see.

I had the same problem programming the 457gw on my 04 Sierra.  When I put a diode in the ground wire from the 457gw everything came to life.  Place diode with the stripe toward the ground connection to the body.

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Bill Lorkowski

place a diode with the stripe towards the body of truck?? Ive never tried that but wouldn't that prevent the ground from being connected at all?!?!

Try to reset the 457G while it is connected take out the fuse and then touch it to where it to the terminals, make so that you are about to plug in the fuse but you don't. The end result will be giving the unit power then disconecting power. Do this for about 10 times and it resets the 457G. Also, when you change out the radio in those cars and it has an info button or traffic button on factory radio, you need a integration harness. Scosche makes them. Ive never heard of taking out a fuse.

This is the link:

scosche integration

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Cruisin Security And Sounds

The gmos01 is the metra version of that scosche piece.  The diode if it's hooked up the way stated will allow the unit to ground.  If its hooked up with the stripe towards the 457g that's when it won't ground.

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Cause I'm So white and nerdy...
First Class Certi-fried installer

Just thought I would chime in I had a  03 trailblazer that would not program up (457gw) and the fix was diode isolationg the ground.

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i apoligize for my post. I was thinking backwards!

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Cruisin Security And Sounds