Everything BUT 4Hi Works

spook1

Original poster
Member
Nov 7, 2012
9
Guys I am new here and tried the search function, but couldn't find anything specific to the issue I am having. Here is the rundown. At first, the only thing actually engaging was AWD. The 4Hi or 4Lo was not working. I pulled the #8 fuse and waited and reinstalled it. After that, the AWD still works, but when I turn it to 4Hi, there is no engaging, and the switch makes no light at all above the 4Hi symbol. The AWD light just stays lit up. However, the 4Lo now works after pulling the fuse and reinstalling. It engages, and the light above the symbol lights up.

I am confused to why the 4Hi doesnt work though, and it is what I would rather have working. My truck is a 2005 Chevy Trailblazer with the 4.2. I plan on fixing it myself (if I can), but didn't know if it would be the encoder motor, or possibly the 4wd Selector switch. I figured I could replace a few parts myself for alot cheaper than taking it to the dealer.

The vehicle has 85,000 miles and I have changed the differential fluid recently. Any help on how to get the 4Hi working is appreciated.
 

spook1

Original poster
Member
Nov 7, 2012
9
Also, I don't know if this would be related, but sometimes I hear a light clicking sound when braking down a hill or even coming to a real slow stop, coming from the right front passenger side. It isn't the brakes making the sound, and it isn't always there I don't think. But there is a clicking noise when slowing down coming from the right front passenger side of the truck.
 

jrSS

Member
Dec 4, 2011
3,950
How many noises are u hearing going into 4 hi?? Should be 2. Try inching the truck fwd a little to see if it goes in while going in 4hi.
 

spook1

Original poster
Member
Nov 7, 2012
9
I hear the front whine going into awd. From awd to 4hi there is no noise or no light change above the 4hi symbol. Basically nothing going to 4hi. From 4hi to 4low, the light flashes and then stays solid and I hear the engagement in the rear of the vehicle. I am just stumped as to why there is no light or noise in 4hi, but awd and 4lo both work. Any suggestions.
 

spook1

Original poster
Member
Nov 7, 2012
9
An update. I had took out the #8 fuse yesterday and after installing it back, the 4lo worked. However, I tried it today, and the 4 lo isn't working again. Only the awd is working. When you switch to 4hi, no lights flash or anything still. When switched to 4lo, the light will blink, but never goes to a solid color, and it isn't engaging now. No noise either.

Do you think it could be the encoder motor and the switch?
 

spook1

Original poster
Member
Nov 7, 2012
9
My fluids have been changed recently. I am going to try it again to make sure I am in Neutral when trying to get to 4Lo. It just has me puzzled as to why everything but 4Hi would work, if I can get to 4Lo again. I am thinking I didn't have it in neutral yesterday. Would the switch prevent any lights above 4Hi, as well as nothing engaging in 4Hi, but AWD and 4Lo work properly?
 

navigator

Member
Dec 3, 2011
504
for 4lo my manual says to be in N and rolling slowly I think 2-4 mph.
I seem to recall Roadie saying sometimes you might have to rock the steering left to right a little to get 4hi to engage.

With the vehicle off, I would cycle the switch a bunch of times, they are known to get gunked up and cycling the switch say 100 times will help clean the contacts.

There is an article on offroadtb that might help

Offroadtb.com Diagnosing the 4WD System
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Welcome! If you edit your profile we will know what vehicle we're talking about faster than scrolling back to the first post all the time.

A 2002 I might consider it a flaky TCCM, but for 2003+, your symptoms do sound like the switch. In mid-2005, they changed it for increased reliability, and cut the price at the same time. If you get one on Ebay, see if it's the new one with international symbols instead of letters for the modes. Or just get one from the dealer - I think they're well under $30 now.
 

spook1

Original poster
Member
Nov 7, 2012
9
Got my profile updated, hopefully. I think I will give the switch a try as it is a fairly cheap starting point.

Can the switch be just pulled out, or does the dash panel need to be removed? I didn't think about the switch actually, as I was just confused why everything but 4Hi would work. I will report back to see if this cures it.
 

spook1

Original poster
Member
Nov 7, 2012
9
Well I changed the switch and everything lights up like it should through all ranges. However, I don't hear the clunk noise from under neath / behind me when switching to 4hi and 4lo. I tried it on the grassy hill beside my house and the front wheels aren't engaging as I was spinning out. I guess 4lo was actually 2 lo as it was geared low, but would still spin the back tires. So I guess it is back to the drawing board. I am thinking maybe it never was going into 4pm before either, just the lights on the old switch were working right.

So do you think I probably need a new encoder motor? That is what I was thinking now, but would like to see before I shell out the coin.

I did pull the #8 fuse again, but didn't unhook the battery. I will try that tomorrow. The switch did need replaced though as I was getting no light when going to 4hi before, but now everything lights like it should.

Any advise?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
If it all lights up, and you hear the expected noises, and no lights flash, then you have a mechanical problem.

Follow the ORTB troubleshooting flowchart. You may have the dreaded splined disconnect failure in the front.
 

spook1

Original poster
Member
Nov 7, 2012
9
I need to run through it again but am not sure if I am hearing the right noise coming from the back. I hear the whinennoise in awd and then some other faint noise when going into 4hi. Anything else I should be hearing.
 

spook1

Original poster
Member
Nov 7, 2012
9
the roadie said:
If it all lights up, and you hear the expected noises, and no lights flash, then you have a mechanical problem.

Follow the ORTB troubleshooting flowchart. You may have the dreaded splined disconnect failure in the front.

Well I am hearing the noises from the front and back. I replaced my switch and now everything lights up as it should as I move from 2hi all the way over to 4lo. But I tried it out on tHe hill beside me and my rear wheels would spin, but the front wheels wouldn't engage. I am thinking it probably is the front axle disconnect. Is there any sure way to tell before I pay the $325 for it from amazon (I guess that is the best place to order it).

As I said earlier, I hear a click noise sometimes from the right front of my vehicle. It is more in the right center, and not as far over as you would hear with a regular hub bearing. It is usually heard when I am going really slow, or when I have the brake about halfway depressed. I don't notice hearing it when I have the brake almost fully depressed. But for example, if I am coming down a hill and slightly press the brake, I will hear it then at around 45mph or so. But I hear it real distinctly when going really slow, and it doesn't seem to matter if you are turning or going straight.

Would the bearing in the front axle disconnect be causing this clicking noise? Any suggestions are greatly appreciated.
 

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