...i'm new...have 2001 blazer. the dash has 2wd light. when going to 4wd auto, i get blinking, as well in 4wh high. both return to 2wd after time. mechanic had it in the air and we could hear it trying to engage but front wheel did not turn. he surmised problem was electrical and i needed to bring it back. i can't hear it trying to engage from inside the truck. i would think it is a good sign that i at least get flashing light. thanks.

 

https://blazerforum.com/forum/tech-articles-diy-29/4x4-no-worky-maybe-will-help-7180/
That should help you out. Its more than likely a vaccum issue, these trucks are know for it. I would find a new mehanic...

 

like i said, mechanic couldn't find anything wrong with vacuum side...so where might the electric gremlin be?

 

Have you cleaned the contacts on the TCCM? Have you checked the actuator under the battery? Or made sure the actuator cable is free and not either disconneted or stuck?

 

Try disconnecting the neg battery cable for 30mins, then reconnect it and try it if it works then it could work forever or it could work for a couple mins, if so it more then likely the transfer case motor/ encoder motor.

 

thank you..i've made a little list. it's going back to mechanic today for pinion seal and serp belt, then a relook at the 4x4 system.

 

the encoder motors can become weak, when the button is pushed the motor will sound like its turning but its not powerful enough to pysically turn the selector on the transfer case. There is a satisfying clunk or click when a shift is made. My old one would hum like it was working but was so weak when testing it i could stop it by hand. Usually vaccum issues with the front actuator will allow the shift into 4x4 but the front simply doesnt engage. Have the front actuator vacuum line tested while the button is pressed. If it makes the shift even for a second it will apply vacuum to the front vacuum line. Make sure it's before any vacuum switches. Sometimes there is one on the fire wall. I'd hook into the one that goes into it. This will at least tell you if the encoder motor is turning the shaft. These systems are hard to test unless you are real familiar with them.

 

one short question before it goes....i had 1 nat'l chain mechanic suggest a new dash 4x4 switch for $ 160 installed. from what i've described ( being able to hear it trying to engage and light switching back and forth) does anyone think the switch is the problem?

 

thanks andrew 01991

 

Umm... No on the new switch for 160, if you can hear it trying to engage, its not the switch... and 160 for a new switch installed? That is just... insane.