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4wd not working no lights on switch.

Old 04-14-2019, 05:02 PM
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Default 4wd not working no lights on switch.

Hey guys, I have a 1999 Chevy blazer 4.3 4wd 4 button switch. It has the vacuum 4wd system. When I got the truck the 4wd never really worked. So I started out working on it. So far I have
1. Replaced dash switch.
2. Replaced encoder motor.
3. Cleaned TCCM connections.
4. Removed battery, checked actuator.
5. Tested new vacuum switch on firewall.
6. Checked all fuses.
7. Hooked battery cables together to try to reset everything..
Here is what I found, no lights work on my switch other than when started they flash. The Service 4wd light is on. It has constant vaccum to the actuator. So my problem is this. When I shut it off it was in 2wd now its stuck in 4 low. No lights on switch so I cant get it to kick out. I dont want to rig it i want to fix it. It has power to the TCCM it has power to the switch. It obviously has vacuum to the actuator which i cant figure out why... any help is appropriated..

Last edited by Nagreene77; 04-14-2019 at 05:04 PM.
Old 04-15-2019, 03:32 AM
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The only thing I can think of that is not on your list is the TCCM itself. I had mine go out. While it was going out, I would hear a bunch of clicking before finally engaging. But eventually I would hear nothing.

Did you replace all of the under-hood vacuum lines while you were at it? You might as well as they will eventually rot away.
Old 04-15-2019, 10:16 AM
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Yes I replaced all vaccum lines all that I could reach anyway.. see I hear people talking about hearing a clicking noise but I dont hear anything from the TCCM or the encoder motor..
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