4x4 self test

[aleekat]

98 blazer, 4x4, 3button 4wd. Searched for previous post on how to test the 4wd system. Vaguely remember, grounding out some pin, then turning the key on, and count the flashing lights on the 3button system. Can someone help?
Which Pin?
Where's the module located?
What do the number of flashing lights mean?
Thanks

[MT-2500]

What is it doing or not doing?
If a 233 transfer case ground pin 13 on diagnostic connector and turn key on and check for shift buttons to flash code.
If all button lights come on at the same time and go out and no more flashes you do not have any codes.
Post back any flashing codes.

[aleekat]

Originally Posted by MT-2500

What is it doing or not doing?
If a 233 transfer case ground pin 13 on diagnostic connector and turn key on and check for shift buttons to flash code.
If all button lights come on at the same time and go out and no more flashes you do not have any codes.
Post back any flashing codes.

The 2wd, 4hi and 4lo work like they are suppose to. What happens driving down the road, the indicator lights(2wd, 4hi, 4lo) start flashing, sometimes all go out, or all are on. The tranny is staying in the set gear.
On a side symptom, I am getting some minor erratic rpms at shifting speeds. Someone mentioned some type of vacuum switch, control switch in the belly of the tranny.

[MT-2500]

Any transfer case code?