4x4 dash lights, sound, does not engage
 

...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...

Thanks but
 

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.

Agreed above....what the mechanic may not know is there is a diagnostic procedure where the TCCM will tell you a few things about what's going on with the 4x4 electronics. This may prevent throwing money at the problem, which is sounds like what he is suggesting. See the DIY section, "4x4 no worky" thread.

Ya, dont think its the switch. Im thinking encoder motor or possible TCCM. It all depends on the test i described.

initial report is that the cable from the actuator is seized.

well some good news i think, but not elated yet. they installed the cable from the actuator and it does engage the front wheels....BUT...the dash lights continue to blink; lights do not go solid...please help as it is up on the rack and they are working on it as we chat.

4x4 DASH LIGHTS LOOK
 

new to forums and don't know how to link together BUT i have thread 4x4 dash lights. to continue, the mechanic installed new actuator cable and the front wheels now engage, turn, sounds good...BUT...dash lights continue to blink and will not go solid. he's working on it as we chat. suggestions?

i had a simialar issue, where I new the front was engaged but no lights or the lights would go off every now and then. Just replaced the switch and all was well.

What about a tccm relearn, I know I say that a lot, but the tccm could still be thinking there is a problem with it engaging, even though it is working, so a relearn could correct the problem.

Sounds like a bad connection somewhere

check the Pins on the encoder motor plug.

i have news....it might be good...and some bad...tomorrow!

Try a TCCM relearn, pull fuse, wait 10 min to make sure it's gonna work, plug it in. see if that works. If not checking wires may be a good idea and could be your problem. Sounds like something isnt telling it to stop shifting. Encoder motor could be bad, wiring could be faulty, or TCCM could be at fault. This system has similar symptoms for multiple problems.

mechanic needed part which i went to pick up....it was oem valve/replacement jobbie that goes on the fire wall with power to the top and two vacuum lines to the bottom, maybe two-three inches high. after replacing it, i immediately had solid lights when selecting auto 4, 4 hi/4l. great.

What is this vacuum solenoid called and does it do ? Also this thread has some great info thanks to all for there input it has been very helpful.