Ive searched everywhere, and posted in both the LT1/Lt4 and auto trans sections to no avail. Maybe someone here can help..

-How does my 96 TA's pcm 'know' when Ive moved the shifter out of park or neutral and into a drive gear?

-Or does it even care whether its in gear or not?

-Dont the M6 pcm's use the VSS at least partially to determine whether the engine is under load or not?

Just trying to figure out whats different in how a M6 pcm does it and how a a4 pcm would do it. My wiring diagrams show a difference in hard wiring, mainly in the PRND switch on the A4 cars. That switch seems to be 3 in one; park/neutral safety, reverse lights, and one more undetermined circuit with 2 wires that get connected/disconnected based on switch position. I have no diagram that illustrates the internal workings of the switch and I dont have one to experiment with.
Im guessing/hoping that these two wires (orange and black) are the answer to my questions.

Thanks in advance,

Justin

 

The VSS is used for lots of things. Imagine coasting down a hill in 2nd gear with your foot off the gas. With no VSS signal the PCM would be saying "why the hell is the engine idling so fast?"

The orange and black wires are the P/N position switch. The input from that circuit changes the idle speed between in gear and out of gear to lessen torque converter "tug".

 

That is exactly the info Ive been searching for!!! Thanks so very much!

As I was doing the nice break-in on the rear and th400, I just had those two wires connected as I did when I originally swapped from the 4L60E to the t56. The idle characteristics were really weird and the pcm seemed to have a hard time with me engaging a drive gear with the TH400. So the PCM was thinking I was in park/neutral when I was going into any other gear.

So basically I need those wires to connect through a relay or something when Im in park or neutral, and disconnect in any other position.

I had another question along with this one that never got answered either... Maybe you can help

If I have the WSS hooked up instead of a trans VSS, will I have issues with a zero speed signal while the car is on the dyno?

Thats just something I would like to know, as my thinking it would be a problem led me to just go ahead and purchase the correct GM parts to adapt a VSS to my TH400.

Thanks Again!