I have been reading all the 4x4 post, but nothing seems to help my problem. I just want to know more before I start spending money.

99 4door
4wd hi flashes then goes back to 2wd
Auto 4wd flashes then goes back to 2wd
I can put it in 4wd lo and neutral

before i crawl under the truck in the snow (or take it to the dealer)
Are there seperat vacuum lines for hi and lo?
If it goes into low, then why not high?

any help would be great,
Industrial Maintenance Tech
with little knowlegde of trucks

G. Webb

 

This sounds like either a TCCM issue or the encoder motor. I would first remove the TCCM (behind the passenger side kick panel) and clean the electrical connection. Also, pull out the switch in the dash and clean the connections into that.

When it goes into 4LO, have you confirmed that the front axle is engaged? Is your 'Service 4wd' light illuminated?

 

I assume that it is engaged.The body of the truck shifts as it engages and I am limited to how fast i can go.
I will check the connections and post what i find.
thanks

 

i dont mean to steal a thread here but i have the exact issue here with my 2000 blazer,coming home in the snow today i tried to get it into 4wh hi,no go,stopped put it nuetral,i could get 4wh lo but no hi,light blinks and goes back to 2 wh hi,yes 4 wh lo was working fine,easy to tell in 6" of snow.no warning of any kind showing.will follow thread,thanks

 

To gewebb,
When in 4LO, does the front axle spin when you punch it on slick surfaces? If not, then check your front axle engagement vacuum actuator for proper operation. Most of the time, this will not cause it to not engage in 4HI or Auto4wd. I am thinking this is an encoder motor problem, but you really should have it properly diagnosed by pulling the TCCM codes (Tech2 scanner or equivalent).

To spitdoggy,
Again, this sounds like an encoder motor problem. If you do not have the Auto4wd option (you'd know if you did), then you can run through the DIY article on OBD2 Non-Automatic Transfer Case Diagnostics.

 

thank you,will work on finding a bud with a scanner.

 

I had a similar issue. There's a solenoid in the engine bay that caused my problems. I pushed the 4hi button, then pulled both lines off of the solenoid, and hooked the "to engine" line up to the other outlet of the solenoid... it cleared it out and it worked again.

Pics:

 

wow,great picts,thanks for this,i assume you switched the hose with the truck running?

 

Yes... truck running and 4hi button pressed.