I just bought a 99 Blazer today. It has an issue with the 4x4 not engaging.

Found fuse #15 blown out. When I tried to replace it, it blew out again.

When it blew out, there were a couple goofy electrical gremlins that popped up at the same time. 1) The fuel guage went empty and the back light for the shift indicator went out. The #s still appeared, but you could not tell be the backlight which gear you were in.

When I replaced the fuse, the above gremlins went away, but the 4x4 still will not engauge. The lights on the 4x4 switch also do not light up.

Where do I start the troubleshooting process ??

TIA!

 

Do you have an ATC fuse under the hood? If so pull it for a minute and then reinstall it your 4x4 system so come back online. If the fuse keeps blowing start unpluging 4x4 components untill it does not pop the fuse. Start with the T-case motor first.

 

Thank you for your reply.

I'm not sure on the ATC... I'm actually picking the truck up today. I'll have to check that.

BTW, what does ATC stand for ?

 

What all components are there ?

After I unplug the motor, which component would be next ?

 

Well, now the Fuse is NOT blowing, but still no Lights on the Switch and no 4x4 function.

How does one get the Error Codes to flash on the 4x4 Switch ?

 

I took it to a local reputable tranny mechanic today who 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 ???