Has anybody heard of a 4WD Vacum Operating Switch? Apparently it is on the firewall I am told that might be the problem why it won't always go into 4x4. It is for a 2000 Blazer 4 Button(N8) If so do you know about how much it would be to buy and what it looks like. I am in Ontario Canada. Thanks

 

It's on the transfer case in the front on the left top. There are 3 hoses going to it and it makes a difference how they go although you really have to work at putting them on wrong. I know. Someone did on mine once. Last time I guarantee.

 

What is it doing? Not engaging? What does it do when it does not engage? Does the vacuum solenoid energize and allow vacuum to pull on the actuator under the battery? If so, then the solenoid is not your problem.

As stated in many other threads on the subject, the NV236 transfer case (4-button RPO code NP8) cannot be diagnosed without the aid of a GM Tech 2 or equivalent full feature scan tool. There are some things you can check over yourself. Those items include checking for corrosion at the TCCM and encoder motor electrical connections. The TCCM is located behind the passenger side kick panel and the encoder motor is located on the driver side of the transfer case near the front driveshaft.

The OP is correct, it is on the firewall when you have the 4-button NV236 transfer case (NP8).

The mechanical vacuum switch is on the transfer case for the NV231 & NV233 transfer cases.

 

The mechanic said it doesn't completely go into 4x4. The lights on the button on the dash flashes but never goes right in. So he said he is going to check the switch but asked me if I can get one in the meantime. So is it on the firewall? If so what does it look like and how much would one cost

 

I doubt you need a new vacuum solenoid, but that would be very easy to check.

The vacuum solenoid is located on the firewall near the distributor. It will have a two wire electrical connection as well as two vacuum lines running to it.

To test it, start the truck and pull off one of the vacuum lines. You will either have vacuum (the supply from the engine), or you won't (the line that runs to the actuator. You want the one that goes to the actuator. With the line to the actuator in your hand, place your finger over the now open port on the solenoid. Have someone push the 4HI or 4LO button. Feel for vacuum pulling your finger against the port. You may also feel/hear the solenoid click if it is working properly. If it does and your finger gets pulled against the port, your solenoid is working properly.

Does it go into 4LO?

 

Yes it goes into 4Lo

 

And 4LO works properly (front wheels spin)? If so, the solenoid is working properly and your issue is likely with the encoder motor.

 

No the front wheels are not spinning. He said the encoder motor is good The TCCM was replaced too because it was no good. When you push the button the lights flash but it never really goes into 4x4. And the lights keep on flashing I took it for a drive and it felt like it when in but the back end still slid when I took off and the front did nothing

 

If 4LO engages and 4HI does not and the TCCM has been replaced, there likely is a problem with the encoder motor. The front axle does not have to engage for it to complete the shift.

And you are taking it to a mechanic who is being this free with your money? Doesn't sound like he is actually diagnosing the problem.

 

No he isn't taking my money. So far he has only charged me for 2 hours labour. He has checked all the wiring and I got him the TCCM from a guy that rebuilds them.He said the motor was working properly. That is when he phoned me and told me about this part on the firewall he was going to check. He said that is the only other thing he can think of. Everything else seems to check out fine. When he took it out for a ride he said sometimes it will go in and sometimes it won't. Any idea how much that part would be?