What is the transfer case VSS used for??

[ntilley52]

I have a 2009 5.3/6l80e swapped into my k5, i used a np241 tcase with an oem vss(40 tooth). My engine\trans came from a 4x4 truck, said truck had a vss sensor in the tcase. I had my harness reworked by current performance(i have talked to them and they dunno). Any way truck runs, drives and shifts fine, they gave me a speedo wire output to hook to my autometer gauge, and speedo is accurate. When i shift into low range, the trans still shifts, it just shifts wrong, it thinks im goin 2.78x faster, which is understandable as it doesnt know im in Low.

I have been reading and it appears that the e38/t43 (maybe others too, i dunno) used the programmed tire size and gear ratio along with engine rpm and internal trans speed sensors to know how fast you are going. to test this i unhooked the oem vss pigtail from my transfer case and it made no difference on how it drives. I have also come to understand that J1 pin 2 in the e38 is 4low signal. So by triggering that it knows im in 4 low, and knows the low gear ratio, and makes necessary adjustments.

So then WTF is the vss in the 2009 tcase for? My assumption is it ran the OEM 2009 speedometer, and the output ive been given from harness rework guys was added in and comes from ECM??

And is there anyway i can make my tune look at the signal from it to control shifts, so that i can run my double transfer cases and still make it shift right?

thanks

[1364838952]

It could have been used as an ABS wheel speed sensor for the rear wheels. If, as you say, it does not affect speed read out on the dash, then perhaps ABS related. Also, it has been my experienced that many T-cases will have MULTIPLE speed sensors in them. Some used to detect output shaft speed relative to t-case range selected. *Usually* the actual OSS on 4x4 vehicles is in the t-case and is what the TCM/PCM uses to detect vehicle speed.

[ScottTX]

First off, I am no expert but what you said here "My assumption is it ran the OEM 2009 speedometer, and the output ive been given from harness rework guys was added in and comes from ECM??" is exactly how I understand it works. In your application with 6L80e, the ECM determines speed and can send that info via a wire to an aftermarket speedo. On the old NP241, the VSS on TC was used for speed. If you had a 4l60/80, you would need the VSS on the TC to shift correctly, but the 6L80e gets all the info it needs to shift correctly in 2wd or 4wd internally.