4x4 Issue on 97 Jimmy

Two problems have recently started with the 4WD. While driving down the road
the indicator lights on the dash will switch over to the 4 HI light from the
2 HI. Pushing the switch on the dash always takes it back to 2 HI. I really
do not think the transfer case switches as there is absolutely no change in
the way the vehicle operates. The various speeds that it happens has been as
high as 70 + mph or as low as 15 mph (always has happened on paved roads).
This has occurred several times in the past month.

The second occurs while troubleshooting. When I push the switch to go to 4
HI it blinks for 15 seconds then switches back to 2 HI. I can not get it to
engage by using various combinations of shift techniques that are described
in the owners manual. If I engage the 4LO it always shifts into gear and
this is confirmed by driving it. When it does shift into 4 LO the 4HI light
also stays lit steady.

The vehicle is a 97 Jimmy with 205K on it. Went through the 4 WD system last
year. Replaced the front axle indicator switch, vacuum lines, transfer case
switch (3 prong vacuum), and the 4wd dash switch (electrical). Just checked
the 4wd actuator motor (vacuum) that engages he front axle. It works
properly and holds a vacuum (tested with a manual vacuum pump). The only
major items not replaced are the TCCM and the Decoder motor on the transfer
case it self.

I have googled and looked for troubleshooting advice from others with this
similar vehicle and have come to the conclusion that one of the last two
items above is intermittent. The durn items are way expensive and I usually
would not trust electrical items like these from junk yards.

1. Is there a way to reset the TCCM for troubleshooting? I have read a
couple of threads that suggested this but could not determine how except
pulling the power. One talked about pulling fuses and cycling the ign.

2. What is your thoughts on which of the above is intermittent?

3. What else have I missed?

As Always,
TIA
GM

On Sat, 13 Oct 2007 16:07:00 GMT, "GM"
wrote:

>1. Is there a way to reset the TCCM for troubleshooting? I have read a
>couple of threads that suggested this but could not determine how except
>pulling the power. One talked about pulling fuses and cycling the ign.

Pull TCCM fuse for about 10 minute and replace it and that will reset
it and clear its memory


>2. What is your thoughts on which of the above is intermittent?

It is likely encoder motor or TCCM itself. Push button 4x4 drive
control looks good on paper and is sales brouchure but can be a pain
to grow old with. You have done well to get service life you have out
of it without a major failure as many get a lot less.

>3. What else have I missed?

Not really
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