Hey everyone new to blazer forum in search of help. My mom has a 99 blazer 4.3l 4wd with the np 233. She shifted it into 4hi one day this winter and now it wont disengage. I can hear the electronic shift motor on the tcase move when i push the 2hi button and then it moves a 2nd time like its engaging 4hi again. It shifts from 4hi to 4lo and back but not to 2hi. ive checked the vacuum lines at the actuator under the battery and everything was connected. To me it seems like the switch is working because its making the shift motor work but im not sure. Any help would be greatly appreciated. Thanks

Geoff

 

Sounds like either the encoder motor is binding up or losing its position signal as it tries to get back to the 2HI position. The picture below illustrates the different mode positions which the encoder motor goes through. As you can see, it rotates from 2HI to 4HI to 4LO. If it has some kind of restriction between 2HI and 4HI, it would not be able to get back to 2HI. If it a channel drops out (position references), then it will revert back to the last selected mode.

NV233 transfer case encoder motor travel:


I doubt that anything is binding up inside the transfer case. Can you get it to return to 2HI by disconnecting the battery for at least 15 minutes? If it does, it is likely caused by a failing encoder sensor in the encoder motor assembly.

 

ive tried disconnecting the battery and that did not make a difference. Is there any thing i can test on the shift/encoder motor to see if its binding or losing its position. if i pull the motor off the tcase and push the 2hi button what should i be looking for the motor to do to ensure that its working properly. Would i be right in betting that the other parts( switch, vacuum, tccm, etc) are functioning properly since the shift motor is trying to work? thanks again for the help

 

DO NOT remove the encoder motor and allow it to run disconnected. You will damage it.

As far as tests that you can do, you could start by doing the diagnostic detailed in the Tech Articles (DIY) section entited "OBD2 Non-Automatic Transfer Case Diagnostics" or something to that effect. See if it comes up with an encoder fault.

 

I grounded pin 13 and the shift lites all blink once every 3 seconds so i think that means it has 1 DTC stored and it would be the RAM Standby power loss right?

 

Yes, that is what it means. So no stored codes other than that. Was a shot at the TCCM telling you what was wrong. You can remove the encoder motor from the transfer case and manually turn the sector shaft (what the encoder motor turns) with a wrench to see how easy it is to move or if there are any rough spots. Mark the position of the shaft before you turn it though.