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99 Blazer 4x4 Not Working...

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Old 08-17-2009, 06:16 PM   #1
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Question 99 Blazer 4x4 Not Working...

I just bought a 99 Blazer the other day. I knew it had an issue with the 4x4 before I bought it.

The lights on the 4x4 buttons will light up (for the quick diagnostic test) and then go out (and remain out) completely. I can NOT activate the 4x4 functions at all using the 4x4 buttons.

The Service 4WD light illuminates after driving about (5) miles or so.

I took it to a local reputable tranny mechanic who then pulled the codes. He got a Code B2725 which mentioned something about a Switch.

The mechanic was able to manipulate the transfer case into and out of 4x4 via the Code Scanner (pretty cool I thought!). So I know that the 4x4 components (actuator, encoder, motor and TCCM) are all working.

He said it most likely is a bad 4x4 Switch. He did mention that his scanner "should" have only been able to manipulate the Auto-Track (NP8) transfer case and not the NP1 transfer case. (Not certain his reasoning though....).

He was questioning whether or not someone "may" have installed the wrong switch. ???? Maybe installed this (3) button switch instead of the (4) button switch.

Now, he crawled under the truck and verified that it does in fact have an NP236 (NP1) transfer case underneath it.

However, the Codes in the glove box do NOT show NP1. There only is an NP8 showing.

He mentioned it would be a significant under taking to change from a NP8 back down to an NP1. Different case sizes as well as different driveshaft lengths etc... So, that would NOT be likely a person changed from stock. ??

I'm thinking about just buying a new (3) button switch and see what happens ??

Ideas ???
Old 08-17-2009, 08:03 PM   #2
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Exclamation Re: 99 Blazer 4x4 Not Working...

According to my research, this is the switch the NVG236 or 236GM NP8 transfer case should have on the dash.



The PO swapped in a 3 button switch in my Blazer.
Old 08-17-2009, 08:23 PM   #3
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Exclamation Re: 99 Blazer 4x4 Not Working...

More research reveals that the 236 transfer case IS actually a NP8 !!
Old 08-20-2009, 09:35 PM   #4
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Re: 99 Blazer 4x4 Not Working...

Yes, the NP8 is most definitely the 236 case, that is what my truck has. They require the 4 button controller.
Old 08-20-2009, 09:46 PM   #5
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Question Re: 99 Blazer 4x4 Not Working...

Quote: Originally Posted by b1lk1
Yes, the NP8 is most definitely the 236 case, that is what my truck has. They require the 4 button controller.
Yea, I just received and installed a new 4 button controller this afternoon.

The 4x4 is now working! However, the Auto 4WD button stays lit up in every mode. ???

Yes, I did pull the 4x4 10 amp fuse and the ATC fuse (for 3 minutes) BEFORE I installed the new 4 button controller.

What would make the Auto 4WD button stay lit up ??
Old 08-21-2009, 07:51 AM   #6
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Question Re: 99 Blazer 4x4 Not Working...

Anybody ??
Old 08-21-2009, 11:31 AM   #7
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Question Re: 99 Blazer 4x4 Not Working...

No decent mechanics on here ????
Old 08-21-2009, 12:25 PM   #8
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Re: 99 Blazer 4x4 Not Working...

You need to get a Tech capable scanner and get in there and look for codes.
Old 08-21-2009, 05:12 PM   #9
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Question Re: 99 Blazer 4x4 Not Working...

Quote: Originally Posted by b1lk1
You need to get a Tech capable scanner and get in there and look for codes.
Already done.

Auto 4WD still on.

Is this perhaps normal ??
Old 08-21-2009, 08:47 PM   #10
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Re: 99 Blazer 4x4 Not Working...

No it is not, I have the same setup on my truck and the light is in the 2WD position unless I change it to something else. I will see if AllData has any suggestions and post back.
Old 08-21-2009, 08:56 PM   #11
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Thumbs up Re: 99 Blazer 4x4 Not Working...

Quote: Originally Posted by b1lk1
I will see if AllData has any suggestions and post back.
I appreciate it.
Old 08-22-2009, 10:42 PM   #12
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Re: 99 Blazer 4x4 Not Working...

I cannot find anything in AllData as to this issue. To me it sounds like a possible switch issue (did you get a used one?) or a wiring issue. I can state for a fact that my 236 cased 4 button 4X4 only lights up the mode that the transfer case is in. The only time my Auto 4WD light is on is when I select that mode. WHen I select any other mode that light does go out.
Old 08-23-2009, 04:56 PM   #13
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Arrow Re: 99 Blazer 4x4 Not Working...

Quote: Originally Posted by b1lk1
I cannot find anything in AllData as to this issue. To me it sounds like a possible switch issue (did you get a used one?) or a wiring issue. I can state for a fact that my 236 cased 4 button 4X4 only lights up the mode that the transfer case is in. The only time my Auto 4WD light is on is when I select that mode. WHen I select any other mode that light does go out.
Thanks for checking.

Would you happen to have the schematics for the TCCM circuit for a 99 Blazer ? If so, could you Email me a set ? -->> Katmandu@woh.rr.com


I have them for an 03 Blazer but it doesn't have Auto 4WD.

The (4) button switch I just installed is New.

I do have a used TCCM here that I'm going to try out soon. I'll post up the results.
Old 08-23-2009, 09:31 PM   #14
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Exclamation Re: 99 Blazer 4x4 Not Working...

Quote: Originally Posted by The_BigBadWolf
The (4) button switch I just installed is New.

I do have a used TCCM here that I'm going to try out soon. I'll post up the results.
Well, the Service 4WD light came on and now it will not go into 4HI.

The used TCCM I have here was the wrong one.

I will get the Codes read tomorrow.
Old 08-24-2009, 09:03 AM   #15
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Re: 99 Blazer 4x4 Not Working...

I sent you the diagrams I could find, let me know if they got through.
Old 08-24-2009, 01:05 PM   #16
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Thumbs up Re: 99 Blazer 4x4 Not Working...

Quote: Originally Posted by b1lk1
I sent you the diagrams I could find, let me know if they got through.
Got them. Much appreciated!

Now, if someone can help me pinpoint the problem.

Last edited by LabRat116; 08-24-2009 at 01:07 PM.
Old 08-25-2009, 01:49 AM   #17
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Thumbs down Re: 99 Blazer 4x4 Not Working...

Still getting B2725.
Old 08-26-2009, 12:39 PM   #18
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Re: 99 Blazer 4x4 Not Working...

I just sent you the troubleshooting flow chart. I saved it as a Word document so if you can't read it let me know and I will save it as PDF.
Old 08-27-2009, 08:31 PM   #19
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Thumbs up Re: 99 Blazer 4x4 Not Working...

Quote: Originally Posted by b1lk1
I just sent you the troubleshooting flow chart. I saved it as a Word document so if you can't read it let me know and I will save it as PDF.
Thank you Sir!
Old 08-30-2009, 09:05 PM   #20
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Thumbs up Re: 99 Blazer 4x4 Not Working...

Quote: Originally Posted by LabRat116
Still getting B2725.
Turns out the Transfer Case Control Module was bad.

I put in another one (same #) and all the 4x4 problems disappeared!
Old 09-09-2009, 09:19 PM   #21
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Re: 99 Blazer 4x4 Not Working...

b1lk1, would that flowchart be the same for a 94 S10 4x4? I need to troubleshoot a similar problem. The lights in my switch will not light with out a lot of prodding. I am thinking new switch but? Also why do you need to take the fuse out is there a capacitor issue or somthing?
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