I just bought a 99 Blazer LT 2 weeks ago and I'm having some trouble with the 4WD system. When I bought it, I was aware that the wheel bearing was worn (howling sound from front passenger's side above 30mph increasing with speed, and it'd fade during right turns), so I picked up a new bearing/hub assembly but haven't installed it yet. Over the past few weeks, I started noticing I'd get intermittent "Service 4WD" notices that increased with frequency, and they would usually go away if I restarted the car. Tonight that wasn't the case though - I was only able to get 4Hi to engage once out of probably eight or nine tries. So I searched causes for the lightto see if my suspicion of the hub was correct and found a response from a mod suggesting that the bearing couldn't be the cause of the problem... is this true?

I feelthat must be wrong, since the bearing and hub assembly are one, so if part of it goes bad, it is feasible thatit would effect its other functions(pardon my ignorance if I'm wrong - my last 4x4 had manual locking hubs, and my expertise lies with Nissan 300ZX Twin Turbos which are different beasts altogether). We have an impending snow here in Chicago, so I'd like functional 4WD... if replacing the hub assembly will do the trick, then I'll do that in the morning; but if it won't, I need ideas as to what will so I can get what I need to fix it as soon as possible.

Thanks in advance for help on this issue. I'll probably replace the hub in the morning regardless, since the howling is getting irritating and I have time to do it, but if that doesn't solve the 4WD problem, I need to know where else to look (search yielded the "TCCM"... which I assume is the Transfer Case Control Module... what, exactly, is this part? The switch on the dash?)

 

Welcome to the forum.
I can't say for a fact if your front wheel bearing is the cause of your 4wd problem but the ABS sensor is mounted in the hub assembly.
I'd replace the wheel bearing and see what happens.
If you continue to have problems you need to read the code to diagnose the problem.
The TCCM is the controller which is located in the passenger side kick panel to the right of the passengers' foot. Rarely does the TCCM need to replaced unless there is a code C0550 or if there is no communication with a scan tool.

Replace your wheel bearing and let us know the results.

 

Well, the light didn't go away completely, but it is behaving better. It's come on less since I replaced the bearing, and when the light comes on, the system still engages. Before, the switch would flash at me when the light came on and it'd eventually just go back to 2WD. Now, it engages 4WD and the light occasionally comes on (but restarting gets it to go away).