I have a 2001 Blazer 4x4 automatic with the 4.3L and the 4 button automatic transfer case. I have a problem where while driving, the speedometer goes crazy, the ABS light comes on, and the transmission starts downshifting. Sometimes it will downshift into 1st and stay there. I have done some reading already and determined that this is most likely caused by a faulty VSS, so I went to NAPA and got a new sensor. I replaced it and had the exact same symptoms. I'm a bit stumped now because it seems like this sensor is the only thing that would affect all three systems.

Thanks in advance for helping a new member!

 

If I remember correctly, there are a total of 3 speed sensors on the NV236 (4-button with Auto4wd) transfer case. Front prop speed sensor, rear prop speed sensor, and vehicle speed sensor.

The VSS has a light green with black tracer and purple with white tracer wire running to it.

Another possible way to identify the proper sensor is that the wiring to the VSS will trace back to a male to male connector body up near the top of the transfer case slightly towards the driver side. I say possible because I am not sure if they phased this connector out in the later models. I remember finding it in my old 2000 AWD Bravada and a friends 1999 Blazer with NV236.