I have a 2000 Trailblazer with AWD. The 4x4 AWD switch is not working, but sometimes it does, but doesn't stay engaged.. Don't know if the actual switch is bad or the actuator. Is there something else it could be? Any help would be greatly appreciated. Thanks, Mike. P.S. It has a LS2 engine with Manguson supercharger and transmission from a 2006 GMC Yucon.

 

Wow! That is one nice looking and powered Blazer!!

First question is what sort of transfer case you do you have? There are three:

• The 3-button, 2hi, 4hi, 4lo (RPO = NP1) two-speed selectable transfer case
• The 4-button 2hi, 4hi, 4lo, Auto 4hi (RPO = NP8) two-speed automatic transfer case, and
• The no-button, auto 4hi (RPO = NP4) awd transfer case used on Bravadas.

As for the 4wd, there are several possible issues.

From what I have seen on the forum, in approximately descending order or likelihood to be the problem, these are the culprits:

• Leaking vacuum lines in the engine compartment. Leaks here can prevent the front axle from engaging and if you have a 3-button transfer case it can also affect it since it uses a vacuum switch. I'm not as familiar with the 3-button ones as the 4-button. Do you have the Bravada transfer case with the one-speed transfer case that is always engaged? When there is a vacuum leak, the HVAC system will often also not be working correctly since the same vacuum supply is used for the HVAC air outlet actuators.
• Bad relays in or bad connector to the Transfer case control module: The TCCM lives behind the kick-panel on the passenger side. When these work correctly, when a change in the transfer case is called by depressing the button on the instrument panel, there will be a single click sound heard. When they are failing, multiple clicks will be heard and eventually no clicks will be heard. Sometimes water gets on the electrical connector and corrosion is created that causes the problem. It is worth accessing the TCCM and at least inspecting the electrical connectors to see if that is the culprit. The selector buttons will blink when the the signal to shift the transfer case doesn't work.
• Shift solenoid(s) in the transfer case: This I have heard of but I am not very knowledgeable of. I think a scanner should set a code if this is an issue.
• Worn engagement gear on front axle. This is part of the gear mechanism that locks the front axle by connecting the right output shaft to the differential. This is not common. It is a chore to fix.
• Bad transfer case control switch in the instrument panel. This is easy to replace but I maybe remember this being the culprit once.

I'm sure there are others who can help too.

 

Not sure which transfer case it is.It is the AWD one. It is out of a 2006 Yucon Denali I believe. I bought the truck the way it is. It has a new hand assembled 6.0 LS2, with Champion ported heads, mild blower cam and Manguson supercharger. It has absolutely zero rust and has 69,000 original miles and was a Texas truck all it's life. It is in pretty much mint condition with super nice interior and has original paint, except for cowl hood.

 

It sounds like you have a full-time awd transfer case like the one in the Bravadas that automatically switches between 2wd and 4wd. These have a clutch system a bit like that in a automatic transmission. These can fail too.

Since the drive train is out of a Denali, perhaps a forum for them and other full size gm trucks would have members more familiar with these systems.

 

If they took the transmission & transfer case out of the Yukon Denali, then I agree with Christine that you might have a full-time awd transfer case and you might not have any controls to worry about. It might be a full-time awd transfer case with a dedicated 40% front / 60% rear torque split and no electronics meaning the switches on your dash are just remnants of the old system that your truck was originally equipped with. The TCCM might even still be there with nothing to communicate with (i.e. no transfer case shift motor). One way to tell what's in it is to crawl underneath and see what it says on the round tag on the back side of the transfer case. I am betting that it is the BW4481 which would have been the RPO code NR3 AWD option code transfer case of that time.

The S-series trucks had full-time awd transfer cases (no electronics - Borg Warner units with dedicated torque splits front/rear) and then they had the smart-trak awd systems in the later Bravadas (NV136 - single speed transfer case with a transfer case shift motor that would move between 2wd & 4wd). I'm not sure that type of setup ever flowed upwards into the full-size trucks.

And I agree, that is a very nice looking truck! Must be a blast to drive!

 

My switch on the dash is 2HI, 4HI, 4LO, and Auto 4WD. I have hardly driven the truck since I got it. The AWD has worked once in awhile, but now doesn't work at all, so I am hoping to get it working again. With 620HP the truck works pretty good in 2WD and hooks up pretty good, but I would like to be able to use AWD because it hooks up great and is really, really, quick out of the hole.

 

That switch might be left over from the previous drivetrain. But then again, it might not.

As Swartlkk suggested, to know for sure, you should go underneath and find the identification disk that will have all the info to tell you what sort of transfer case you have.

Once we have that, the diagnostics can begin.

 

Thanks everyone for the replies. I am going to have to do some more research and follow up on your suggestions and check everything out. Thanks again, Mike