hey everyone, i'm new to the forums, my brother just bought a 99 Blazer and his 4wd doesn't work. The guy he bought it from said the 4x4 control box was broken but i suspect bigger problems. Firstly the SERVICE 4WD light is on. Secondly he had the control box disconnected. When you connect the box the 4HI light blinks and you can hear the relays in the control box clicking, Then when you try to push any other button(auto, 2hi, 2 low, 4 hi) I can hear what I guess is the transfer case solenoid(the black cylinder sticking out of the transfer case) buzzing for about 3 seconds then stops. Every time you hit one of the 4wd buttons it buzzes then stops. In my troubleshooting i did manage to get it into 4HI however the dashboard or the 4x4 switches did not indicate. So i assume the Transfer case itself is fine. I just have an electrical problem. Any ideas? btw, i have plenty of other problems to fix as well but 4x4 just seemed the most important lol. Thanks in advance!

 

If the service 4wd light is on, you should have the codes read by someone with the right scanner (tech 2 scanner iirc, but not 100% sure)

 

Yeah I know, I was trying to avoid taking it somewhere though and paying a diag fee.

 

When it's in 4WD is the front axle locked in? My guess is the encoder is bad and it doesn't know what range it's in. My controller didn't buzz but I could hear replays click (and see the dome lights dim). 3 tries and it would default back to 4WD. It's an expensive part to just hope and throw at it but....... What you call the transfer case solenoid - the black part is an electric motor and the encoder is a set of sensors that lets the motor know where to stop for a given range. It's replaced as a unit.

 

Well something similar happened to my truck and i just did 2 things that fixed it without spending any money.

1.- The clip of the actuator under the battery was really weak, looked for the part in autozone and it cost 12dlls the pair, i ended up using a keychain O ring and pliers and shaped it like a D, it works perfectly and is stronger than the OEM clips.

2.- Cleaned all the 4x4 systems conectors with dielectric cleaner, all of them, TCCM module, TC motor, Dash switch, etc.

Do this first and you may fix it too, i realized that the conectors build up some kind of tick screen, its like burned electric grease, transparent, but dielectric dissolve it pretty well and everything its working again.

Good luck.

 

Had a very similar problem as this, and what the OP describes. Relays would click, I could hear the servo motor spin for about 3 seconds, then stop. Dash lights say stuck at 4WD Hi, but transfer case was actually in 2WD. Battery would drain overnight.

I took the front shaft off, then removed the encoder motor. I could turn the gear that turns the transfer case shaft by hand (which you should not be able to do). So, I replaced the motor unit. I separated the old unit, and the gear was busted in half.

 

It never actually indicated a solid light for any 4x4 mode, it just blinks and after a while goes out and won't respond unless I restart the truck. I also couldn't get the dashboard to show anything, just the 4x4 controls lit up. I haven't had a chance to look at it since this original post but all this info is helping!!

 

If the service 4wd light is on, that means that the TCCM has stored a code which will lead you to the source of the problem. Get the TCCM scanned for codes and let us know what they are. You will need to find someone with a full feature scan tool that can access the other systems in your truck. A generic OBD2 scan tool cannot access the other serial communication devices such as the TCCM.

 

Got the codes read and like an idiot didn't write them down. I do remember he said the front axle and rear axle speed sensors were throwing a code and there was one other which is escaping me at the moment, so 3 in total. I think the third code may have been something about the transfer case gear indicator? also as I pulled it into the driveway the check engine light came on. Lastly, i did a very quick look over to make sure the nothing was disconnected or had a broken circuit and everything seems to be good. While i was under there, on a hunch, i tried to sin the from drive shaft with my hand and couldn't so now It's also stuck in 4wd to top it all off. Any more tips would be greatly appreciated.

 

Really need the codes to help further.