4wd system operation 98up Blazers

[Barnes888]

Hey guys, i've read over this article and i think i know whats going on here. But i seem to have a bit of a different problem on my 2003 GMC Sonoma 4x4 non-Zr2. My truck 4x4 lights all work, and i can go from 2HI to 4HI no problem. As well into 4LO. The problem comes when i go to shift from 4HI to 2HI while driving. The light will change on the dash, but then it doesn't seem to want to disengage out of 4HI straight away and after a bit of time, the front end will suddenly pop/clunk and it will then be in 2HI. I havent had time to pull the battery out yet and check the vaccum lines nor the actuator. but if anyone could point me in any direction of where to look (saving me abit of time) it would be greatly appriceiated.

Thanks!

[reb78]

I'm having some issues with my '99 Blazer as well....When I push the button for 4hi, low or auto, all it does is blink lights at me. I have replaced the TCCM, encoder motor and actuator. Any other suggestions besides taking it to a dealer. I'm pretty good at DIY so I would like to do as much of the work on my own as possible.

[tim153]

My 98 Jimmy has issues going into and out of 4WD. I have read over the forum but dont see anything like the problem I have. I have 3 buttons ont he dash. When in 2WD and push the 4WD button both lights flash. It stays in 2WD untill I slow way down (under 5 mph) It will go into a neutral and then a loud clunk and it feels like someone hit me in the rear end. I have it in 4WD now but scared to try putting it back into 2WD.

[markdw]

Hi Guys,

Newbie here, I was wondering if anyone knew of a source for the pins on the connector that goes to the TCCM mine is completely corroded. Anyone know a site or a part #?

Thanks,

Mark

[spenser]

YOU GUYS ROCK! Had an Ice storm here in Pennsylvania this morning. Hit the 4 wheel drive button and nothing happened! Read this link found the vaccuum line off the selinoid that is mounted on firewall. Splice a new piece in and HOORAY! 4 wheel drive is back on!

Thanks Much!

[ColonelT]

Hello world :]

Excellent post muddog, Thanx! I'm having a little trouble myself and unfortunately the detailed description does seem to cover my symptoms

I'm experiecing intermittent 'Service 4WD' at start up. Sometimes the system works just fine and others... at startup I can see the dash switch lights quickly flash and then it throws the light. The vehicle seems to retain the last configuration actually selected during a function system. It's as if at start up the system is trying to determine the actual current 4WD configuration. And, is if when all sensors or whatever report back normal, it works. But sometimes not it'll quickly throw S4WD.

Literally just before this post I noticed JaVeRo's post about a little newer model transfer case vacuum switches causing probs with the HVAC. I too am having difficulty with my AC. Heat more or less works but AC not. I thinks its a vent door thats not functioning properly automically. So, I merely note the commonality to my troubles and hope for someone's knowledgable input.

Thanx in advance!

[ColonelT]

Pardon me, I thought this forum would automatically attach my vehicle info from my registration:

1999 GMC Jimmy SLT
4D 4WD

[snorander]

Originally Posted by Leifmb

That switch is located above the distributor on the center (engine side) firewall.

Seriosly can someone take a picture of this in the truck I can't find it in my 2001 JImmy 4x4 (3button switch) All that is on the firewall above my distrubtor is the wiper motor!

Steve

[snorander]

Double post, but I can't find this on my truck the only thing on the firewall above the distributor is the wiper motor. Can someone get a picture of where this is located under the hood?
Thanks,

Steve

Originally Posted by laxman21

Here was my problem.



On 99up there is an additional vacuum switch on the firewall that switches the vacuum on and signals the TCCM also.

[gokusupersaiyen]

snorander,

I have a 2003 ZR2 S10, it does not have the "vacuum switch" either. My four wheel drive would not engage but the lights on the buttons would act like everything works, I could hear the tccm click and a motor move but no four wheel drive. I replaced a vacuum hose to fix the problem. It is the one in this photo ( http://www.kylestubbins.com/files/im...zer_vacuum.jpg ) that leads down the center of the firewall. From there it does not go to a vacuum switch, but to a line near the transmission on the passenger side. Mine had come undone at an elbow near the right header/oxygen sensor. Let me know if that helps if not I will try to post a picture.

[snorander]

Thanks gokusupersaiyen, greatly appreciated!

[laxman21]

That vacuum switch is from the 4 button 4x4 system.


Not sure if the 3 button uses the switch.

[woods80513]

Sometimes when I start my 99 Blazer the Service 4WD light comes on and then goes right off like the other dash warning lights. When it does this properly the 4 button switch seems to work properly and I can change from 2WD to Auto or 4WD as normal - the appropriate button is lit up.

But sometimes when I start the car the Service 4WD light goes on, blinks off, and comes back on and stays on. When it does this there are no lights on the 4 button switch and it does not switch from 2WD, Auto, 4WD, etc.

It seems to matter if I turn the ignition on and wait about 3 seconds before starting the car. When I do that, the thing work properly (most of the time). But it's when I just turn the key and start the car immediately that the Service 4WD light stays on and the switch malfunctions.

Any guidence? Much appreciated.

[danbassboy]

the 2 vacuum line and 2 wires image

[snorander]

so I had the battery out and checke out my actuator. I can't pull the cable at all. The actuator will hods vacuum if remove the vacuum line & put my thumb on it so the actuator is good(I assume). Now for the million dollar question....How can I fige out if the cable is siezed of if the encoder motor is seized?

Thanks,

Steve