99 Blazer 4x4 Not switching

Hoping you guys can help me diagnose this.
I have a 99 blazer that has the electronic switched 4x4. (it has auto,4 lo, 4 hi, and 2hi). Slowly the system stoped switching. A
first it would go into 4 high when you hit the 4 auto button. After months or so it just stoped all together. I seem to recal hearing switch under the dash when it was working. It no longer works at al anymore. The service 4x4 light is on. I talked to a dealership an they say it could be a number of different things. Specifically th control module, solenoid encoder, transfer case motor. I think th module in under the dash, but im not sure about the others. My proble is these parts are not returnable because they are electrical. Can yo guys give me some tips to narrow down this problem?
Thanks,
Mik
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u have what is called shift on the fly 4 wheel drive and normally the motor on the transfer case is where the problem is.if you can get access to a snap on scanner with updated cartridges you can scan what is called the GEM module which controls the 4x4 it should give you any codes stored in the gem module. check the codes and repost them may be able to help you better that way

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Very common problem with this system-- remove the right kick panel under the dash on the passenger side-- the 4X4 control module is located here-- disconnect the battery and remove the module and unplug it-- look at the plug as well as the pins in the ecm for corrosion i.e. green wires, rust, or evidence of any water getting into the plug or module-- if evidence of water is found, replace both the plug and the module---
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toyota1 wrote

Must be a common problem where you are, but I've hardly seen what you describe. Most problems with these systems are usually the encoder motor on the t/case.
Ian
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We have the same problem with our 99 Jimmy, switched slowly at first now didnt switch at all, The control module is bad, and ours has the hard to find 4 switch system with auto 4x4, so be expecting to see at least a 400 - 500 dollar price tag when you find this part new, as for a used one, I live in indiana and havent found one in the state.

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I have yet to see one with the bad motor-- had 5 or 6 in the last few months with the ecu plug rotted-- gm has a tsb out on this-- 1 of these was a bad vacuum solenoid=
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toyota1 wrote:

Can't see any TSB out on this...other then guidelines about why "not to replace" TCCM's. I've seen plenty of the bad vacuum solenoids...and plenty of encoder motor failures. Maybe the corrosion problem is related to a different climate. We have quite low humidity here in Calgary...so maybe it's not a common problem here because of that.
Ian
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Possibly so, or maybe the tsb wasnt issued in canada? I got the tsb information and part#s to repair the problem from our service program on the first one-- they use alot of salt on the roads here-- so if any water gets in from outside into wiring- its history-- + anything that may condense from some of the temp changes we have--
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I checked my plugs and they are in good shape, the dealer took the tccm out

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Ours didnt have a TSB out on it either and I live in Indiana

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I dont know what to tell you there-- there is a letter on this-- maybe it has been superceded--??
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hard telling, I know when I called to get a price on the TCCM, I asked for all TSBs for the vin number on my truck. This is a common problem that has happened to the 99's mainly the ones with the auto 4x4 (4switch) system.

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Thanks guys I will try it when I get home tonight and let you know.
dont have a scanner though so I will look at the module and it connectors
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Ok just took the control module out. It doesnt look like the wires ar
rotted. I had the battery disconnected for a bit and when I connecte it the lights on the switch went on. It still wont swtich out of 2Hi but now at least the lights are on.
Any suggestions on what to do next
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mester wrote:

Really....without scanning for codes, you are just stabbing around in the dark. If you can pull code/codes out of the atc module, we might be able to at least point you in the right direction.
Ian
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