I have a 1998 Blazer with 4 wheel drive. I had the P1870 code for a couple years, which just means a transmission component slipping. I finally broke down and got the tranny rebuilt last week. The guy said the forward clutches were burned, and the torque converter was blue meaning it had overheated.
I need to call the guy back because an issue has popped up. It ran fine all weekend until yesterday evening. I started to hear a whine/groan, I only hear it when the vehicle is in gear and between 0 and 30 mph or so, the groan will continue right up to the point where the vehicle stops, like at a stop sign or in my driveway, kind of like a winding down noise.
I don’t think it’s a wheel bearing groan because there is no change in pitch, etc when I turn the steering wheel.
Sunday I changed the fuel filter, plugs, and wires. It runs much, much better now.
I do have an issue with the 4WD, last fall the #15 fuse for the 4WD blew, and now I found that the 20 amp fuse in the under hood junction box was blown. I’m thinking I maybe have a bad connector at the encoder motor. The Blazer sat for a year so maybe some corrosion developed. That 3 button switch is in a bad place for me, sometimes my big fat hand hits the 4WD button when I shift out of park.

 

Can you get it to engage in 4wd? If you can, does the noise go away? If it does, then you likely have a problem with the front axle engagement system where it may be trying to pull the cable even while in 2HI. OR the cable could be partially frozen not allowing the engagement fork to return to its disengaged position.

As far as the fuses for the 4wd system, diagnosing that should start with disconnecting each connection at the various components (switch, TCCM, & encoder motor) to inspect for corrosion. Corrosion can set in regardless of vehicle use, so that's where I would start.

You can check out the various NP233/NV233 threads in the Tech Article (DIY) section for more information at your leisure.

 

Thanks Kyle,
I do think now the fork is engaged or partially engaged, the question now is how to get it to unengage. It's my own damn fault, the car sat for a couple years not running and it just causes more problems then I could ever imagine, especially with the 4WD system. I know so little about these 4WD systems to begin with.

 

Have a read through some of the threads in the Tech Article (DIY) section for some more details.

 

I read through a lot of the stuff on here, and there is a lot of info trying to to let it all sink is tough. I checked my actuator cable and it looks good, took out the sensor and the ball moves in and out pretty good. I pulled the transfer case switch out and the ball was real difficult to move in and out at first but than it got easier. After I put it in I did not blow a fuse when pressing the 4HI button, the actuator sounds like it is working solid. It did not sound like the front axles were engaging all the way or as well as they should, but than the fuse blew again. I am going to replace the transfer case switch today with a new one. Not real easy to thread that switch back in. I'm pretty lucky my son works at Autozone so I get a good discount on this stuff. I may pick up an encoder motor today I found some used ones with 87K for less than $40, but I'll see.
Thanks for the help Kyle.

 

just curious, did your whining noise start before you ever messed with or engaged the 4WD ? and does your whining happening in park to at idle?

 

No the whine started after I accidently hit the 4WD Hi button. I blew the number 15 fuse when I engaged the 4WD and I blew it repeatedly. I just had the tranny rebuilt so my first thought was something was up with the tranny but I found out that was not the case. I replaced the 4WD vacuum switch on the transfer case and I replaced the actuator cable.
A mouse had chewed through the plastic coating and rusted/corroded the metal. So what I think happened was that the front fork did not disengage all the way causing the whining.
But it only whined after the truck was driven a long ways, it had to get 'hot' or something. So it never whined in park, it just sounded like an airplane winding down when I was coming to a stop.