1999 Jimmy 4 wheel Intermittent

Hi, I`ve been having a problem with my 4wheel drive and, before I start parts changing, I figured I`d ask. What`s happening is that my Jimmy is dropping out of 4 wheel into 2 wheel. It`s intermittent, happens more often
when its colder outside, dash "service 4 wheel" comes on, and I lose 4 wheel. Happens in both Auto and 4High. Can be reset sometimes by restarting the vehicle, other times not. A borrowed scan tool shows no hard codes but I havent been in a situation to hook it up when its happening. I`ve heard that the dash switch is problematic in this model with the Auto 4 wheel but was under the impression it was a complete failure problem not an intermittent one. Ive done a good visual on the undercarriage,wiring to the T/case looks good. Any thoughts on how to proceed from here? Thanks Jeff Any thoughts
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JKBK wrote:

of common for the switch to get flakey.
It could also be a problem with the front clutch pack itself. When was the last service of the front axle?
--
Steve W.
Near Cooperstown, New York
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Aside from an oil level check (and the usual tierods, ball joints, etc.) in the summer, I havent done anything with the front axle since I got the vehicle in 2005. Would a front axle slipping cause a system fault? I would think it would no actual 4 wheel. With the intermittent nature I dismissed a mechanical problem with the T/Case or front end and leaned toward electrical especially with some basic research indicating the problemic behavior of the system.
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JKBK wrote:

The way the auto 4x4 works there are a lot of items that can cause system faults. The switch and TCCM along with the front clutch packs are the common fault areas. If the scan tool you borrowed may not be able to read the codes from the TCCM. If the light came one there will be a code stored. You might want to take it to a dealer/independent who has a factory style scan tool. That way to can find out what it is doing.
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Steve W.
Near Cooperstown, New York
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Thanks Steve It was a snapon series scan tool from the local high school mechanics program which is why I`m perplexed as to no code. It is working properly as it is showing a code for my fuel sending unit but nothing else. I understand the TCCM is by the front axle T/C output but I`m hearing clicking in the glovebox area when I`m having the trouble. Is there a module under the dask that controls the system/TCCM? Jeff
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JKBK wrote:

The TCCM on that rig is behind the kick panel on the passengers side. It may be what you hear clicking. It is possible the contacts have gotten corroded casing a problem. The T/C Encoder motor is on the case. http://www.kylestubbins.com/node/11 has a nice write up about the connector.
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Steve W.
Near Cooperstown, New York
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Thanks. In light of the clicking and the TCCM location, that seems like the best place to start. Merry Christmas Jeff
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