98 blazer 4 wheel drive not engaging
 

Hey Ive been trying to solve this 4 wheel drive issue by myself for the past few weeks and haven't had any luck. As of now when ever i press the button to go into 4hi or 4lo the 4 wheel light will blink a few times and it will go right back to 2 wheel drive. You can hear the clicking on the TCCM on the passanger side and there is no other engaging noise in the transfer case and theres no air going threw the vaccum so im assuming its just electrical. I replaced the TCCM, vaccum hose switch on transfer case and the push buttons on dash. I also took apart my encoder motor on the case cleaned it out and seen no problems. also theres a problems with my upper screen where it shows the temperture and compass it flickers on and off randomly and im thinking it could be linked to my 4wheeldrive shorting out maybe? thanks!

I saw you checked the vac lines. Did you check the actuator under the battery tray? I dont know about the elec with your overhead though. I know mine did something. Similar when the vac line going to that actuator rottes out on me.

My actuator works fine, i disconnected the vac line that goes into it and no air goes threw it. Its something wrong in the early stage of the system before the vaccum engages.

I'm assuming you have a 3 button 4wd system. When you push the buttons you should be able to here the encoder motor on the transfer case shifting positions. If you are only hearing the tccm click, the encoder is not operating. Again this is assuming you have a 3 button system.

If the switch on the front axle housing is not tripped when you select 4WD, the TCCM will default back to 2WD.

With the engine at idle: When you select 4WD, the vacuum switch on the transfer case supplies manifold vacuum to the actuator under the battery tray. The actuator pulls a cable that operates a clutch on the right front axle shaft. When the clutch is engaged it trips the switch and 4WD is engaged. When you select 2WD, the vacuum must release the actuator immediately.

I had this exact same problem. reason you are not hearing the encoder motor is b/c you probaby have the car running, it's very hard to hear that little motor engage over the noise coming from the engine.

i can almost guarantee you it's a bad vacume hose.

do this

turn the ignition key to start but dont actually fire up the engine. while sitting in the driver seat open the door and now hit the 4 HI on the dash switch. without the engine noise you should now be able to hear the encoder motor turn and engage. hit 4HI and 2HI a few times. If you hear the motor working but the 4HI is just blinking you probably have a bad vacume hose.

when I had this problem, each component of the 4x4 system worked individually, but when put together i still had no 4x4..........after inspecting all the hoses I found that the vacuum hose going to the air balloon under the battery was broken. replaced it and everything worked fine.

Check the vac line at the fire wall as well

Damn u have a quiet encoder motor then, I can hear mine when i engage it LOL.

I am having a similar problem where the 4wd circuit is shorting and incidentally (like you) the temperature/compass digital readout is not working right. Mine doesn't flicker but rather read "--" for all of the information.

I'm trying to find complete diagrams of the 4wd circuit to see where the Gauges circuit (4) may coincide with the 4wd circuit (15). That would explain the unusual gauge display and the 4wd shorting.

I'll let you know if I find anything that helps. Good luck!

i guess so. i thought mine was dead, i couldnt hear it engage over the engine noise. turns out it was just very quiet. I read on some other forum to try engaging it with the engine off so that way u can hear it better. worked for me. :icon_playing: