1996 Yukon 4X4 Vacuum Actuator Solenoid / Flashing lights ???

[Calderone]

Hi everyone, we were testing the 4WD which we never use and the switch is getting flashing lights.
We did a lot of upgrades last year, the truck is running real good but yesterday we wanted to use the
4WD and it seems it's not fully engaging guessing by the flashing lights, but the transfer case makes the clunk, so we have a really small problem here but I want to discard some small issues.
When we started using the truck we forgot to connect this solenoid:

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It goes in the firewall connected to a pigtail, we cannot find the vacuum lines that go in there.
We have other candidates for the problem, maybe it's those lines?

1 - The push-button switch itself in the dash
2 - The 4WD Actuator

But i want to discard that the 4x4 maybe is not fully working due to the small vacuum lines.
Thanks in advance!

 

[east302]

That kind of looks like the solenoid for the water valve. It’s on the passenger firewall near the a/c accumulator.

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It has a hard vacuum line connected across the intake to the PCV and another line connected to the water valve on the heater hoses.

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When the dash panel temperature dial is set to the “max” cold detent, the solenoid is energized and closes the water valve. This shuts off water to the heater core to maximize a/c performance.

Sorry, I couldn’t help with your transfer case question, but believe you can rule the solenoid out. To my knowledge, the transfer cases have no vacuum actuators.


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[Calderone]

Thanks East, we were thinking that was the 4X4 since it's sold like that on Ebay, my bad

 

[deven bullis]

Thanks East, we were thinking that was the 4X4 since it's sold like that on Ebay, my bad

The flashing lights on the switch means it’s a attempting to engage 4x4, on these trucks length of time for them to engage also depends on how hot/cold it is outside. Do all the lights on the switch work? Because I had a problem with my 4x4 not working and I ended up replacing the switch and it solved all the problems


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[Calderone]

Yes all the lights work but they flash, except 2HI that's steady, the switch is one of the suspects

 

[deven bullis]

Yes all the lights work but they flash, except 2HI that's steady, the switch is one of the suspects

Have you checked the actuator on the front diff? That’s also a big trouble area too.


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[Calderone]

Yes one of the two is what's causing this, thanks!

 

[deven bullis]

Yes one of the two is what's causing this, thanks!

Awesome that you found the problem, hope you get it fixed soon!


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[Rahooo]

Yes one of the two is what's causing this, thanks!

Have you been able to solve the issue? My Tahoe does the same thing and I've got brand new actuator and 4wd switch but still flashes and clunks