Hi all, new to the forum and a new owner of a 99 blazer.

About the only problem I've been able to find with the rig is the fact the 4wd won't work. I've scoured the internet but not been able to find anybody with the exact same problem as me.

When you start it up, all seems normal. No Service 4WD light, the 2H light is on solid. If you press any other button (Auto 4WD, 4H, or 4L) the "Service 4WD" light comes on immediately, followed by a single click from the p/s kick panel (TCCS?). Whichever button that you pressed, it's light flashes. It will keep flashing forever probably (I've only let it for 2 minutes). If you press 2H again, its light flashes once or twice, then goes solid, along with a few clicks from the p/s kick panel.

So far I have to check: Vac Connections, Cable Movement, and all connections. Oh and find a scan tool, any other suggestions?

 

The TCC (Transfer Case Control) module down by the kick panel could be out. Take the Kick Panel cover off and you'll see the TCC, take the connections off the module and look for corrosion on the pins.

 

any resolution to this yet? i have encountered the same issue only no service 4x4 light. Push button, at first i heard a click, the light would flash, then go back to 2wd.

Im worried as i recently changed the T-case fluid. The dealer seemed to have no idea what went in there but gave me the auto trac 2 stuff. This is a 3 button. Said it would be ok either way. Another thing that worries me about it is when i changed it i must have drained 4+ quarts out of that thing. But BARELY managed to get one quart back in. Another thing the dealer couldnt give me is a capacity on the thing. I see a lot of people say they buy 2 quarts to put in it. but never say how much the thing actually holds.

 

Your input shaft is leaking, causing tranny fluid to force its way into the t-case. There is an oil fill bolt on the back side of the t-case (not to be confused with the oil drain bolt...lol). You just put oil in the fill bolt hole until oil drips out. I think 2 quarts is probably reasonable. On my '96 Sonoma, about 2 quarts poured out when I unbolted the fill bolt. Probably means I had darned near a gallon of fluid in there. Check out the pics (scroll down a little).

If your t-case was that full of fluid, that can be hard on the seals of the t-case vacuum switch. It's possible you have fluid in your vacuum lines. In my Sonoma, tranny fluid migrated into the 4x4 actuator under the batter tray. The diaphragm was quite full of oil. The vacuum system tends to leak quite a bit if fluid gets in the lines.

Also, transmission fluid is find for your t-case. I believe the special stuff is for the AutoTrak models.

 

blazerzr299, the OP's system is a 4 button Auto 4WD, yours is a 3 button selectable 4WD, totally different systems & transfer cases. Best to start a new thread to avoid confusion in diagnostics. In a nutshell, the root cause with yours is a leaking vacuum switch on the transfer case.

 

So, further investigation today. Today I pressed 4HI, and wasn't able to get 2HI to come on solid again. After a shutoff and restart, 4HI was now solid. Still not able to get 2HI back on. After pressing auto 4WD and then 2HI, it came on again slid.

Here's the kicker- the front driveline won't turn. I think either the front end or transfercase is stuck in 4hi. The vehicle drives okay but I have noticed cornering tight it binds- telling me the front axle won't unlock.

Any suggestions? Tomorrow I'm planning on pulling the battery & tray and checking the actuator.

 

Well I couldn't leave it alone so I went out and tinkered.

It was dark so I couldn't see well, but I unplugged and replugged the TCCS. I think thats got something to do with it, cause for the first time I got the rig to shift into 4LO. Whether it had front axle engagement is yet to be seen, but it was in the lower gear. The light however, still flashed. I also got Service 4WD immediately upon pressing any button.

I found my solenoid for the front axle. Tomorrow, I'm planning to properly inspect the connector for the TCCS and repair pins if needed, followed by chasing that vac line.

 

Well the pins looked fine, couldn't see any sign of corrosion. I took it to a shop and had them pull the codes. I didn't write it down, but it had something to do with front axle engagement voltage high.

So I figured it had something to do with the vac switch. Once back at home I unplugged the actuator side hose and had my fiance press the 4HI button. No vacuum was felt. Verified good vacuum on the other side. Just for laughs I used an adapter and put the two hoses together, effectively overriding the switch.

I pressed the 4HI button, it blinked twice and went solid Auto 4WD and 4LO worked too.

My next step is to grab a different switch and try that. If that's not it, I fear the wiring may be to blame :O