VSS issue in 6.0 swap in 94 4x4

I need help figuring out how to properly wire the vss up. I have nelsons harness. It has 3 speed sensors but only 2 of them are used. The very front one isnt used because it is a 4x4 truck. My truck uses the 2nd ( plugs into end of tranny, and the third one plugs into the transfer case). My problem is truck doesnt want to shift out of first. You have to manually shift it yourself to get it goin, then its fine. I am gettin a code on the scanner saying vss circuit bad signal so I know something is wrong. Please help with input for a 4x4 truck! Thanks

You will use the front one for sure, near the bell housing; it's the iss, input speed sensor.

Use the second vss on the transfer case.

Ignore the the sensor or plug on the 80e tailshaft.

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Originally Posted by farmtruc

You will use the front one for sure, near the bell housing; it's the iss, input speed sensor.

Use the second vss on the transfer case.

Ignore the the sensor or plug on the 80e tailshaft.

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And thats it? Dont tap into any stock harness wires or anything?

That will get the trans and engine working together, shifting.
Then use the vss output wire from the PCM to the speedometer.

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Originally Posted by farmtruc

That will get the trans and engine working together, shifting.
Then use the vss output wire from the PCM to the speedometer.

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Ive had the truck running for almost 2 years now, and just dealt with the issue. But now Im ready to dig into it. I called a long time ago and I think I spoke with Ray about connecting your vss connector (new style) to my old transfercase. Since the 2 have different plugs, He said cut my OBS pigtail off and put it on the nelson harness. Was that correct? Thats what I did, but it never solved the problem, and I kind of just forgot about it.

Ya that should work. Should be the same type of sensor just different looking.
Any dtc's?

Like wrong gear ratio or input signal?

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Originally Posted by farmtruc

Ya that should work. Should be the same type of sensor just different looking.
Any dtc's?

Like wrong gear ratio or input signal?

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The only code I get is Vehicle Speed sensor circuit. Cant remember the number.

I plugged nelsons vss in the back of the tcase and it will shift by itself, but then my speedo doesnt work

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Originally Posted by HPICamaroSS

The only code I get is Vehicle Speed sensor circuit. Cant remember the number.

I plugged nelsons vss in the back of the tcase and it will shift by itself, but then my speedo doesnt work

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And I have the speedo wire hooked up

Where do you have the speedo wire tied in? On my 1994 I originally hooked it in before the drac/buffer, and it wouldnt read correct. I bypassed it and went straight into the cluster bypassing the drac/buffer and it worked great ever since. I sold the truck to my friend or I would go get the wire color.

Speedo wire should come from the PCM. The VSS wires go to the PCM and the PCM processes that info and sends the signal directly to the speedo on another wire. Should be a dark green/white wire from pin 50 of C-2 connector(Red or Green,depending on year).

So the trans is shifting good now that the speedometer wire is disconnected?
Check pin location and do the suggested above. We've done it that way like others have and it works.

Let us know

I found my diagrams, here's how mines wired.
Green wire pin 50 on the green or red pcm connector, then behind your glove box, find the light blue wire coming out of the drac, pin c15(this feeds directly into the cluster). I clipped this wire and spliced it straight into the green wire from pcm pin 50.

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Originally Posted by slow94

I found my diagrams, here's how mines wired.
Green wire pin 50 on the green or red pcm connector, then behind your glove box, find the light blue wire coming out of the drac, pin c15(this feeds directly into the cluster). I clipped this wire and spliced it straight into the green wire from pcm pin 50.

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+1 to the above.

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Originally Posted by Mickeymotormount

Speedo wire should come from the PCM. The VSS wires go to the PCM and the PCM processes that info and sends the signal directly to the speedo on another wire. Should be a dark green/white wire from pin 50 of C-2 connector(Red or Green,depending on year).

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Thanks! thats a very good tip right there, exactly what I was looking for! So on the transfercase what are the 2 sensors? I am pretty sure the very rear one is the vss whats the one before that. Do I do anything with that first sensor on the tcase?

The first sensor/switch on your transfer case is used to engage the 4wd actuator in your front axle, it also illuminates your floor shifter, and signals the pcm when you have shifted to 4lo, it also has some function for 4wal/rwal.

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Originally Posted by slow94

The first sensor/switch on your transfer case is used to engage the 4wd actuator in your front axle, it also illuminates your floor shifter, and signals the pcm when you have shifted to 4lo, it also has some function for 4wal/rwal.

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So I just leave that first sensor alone? Dont do anything with it?

Just to make sure we're talking about the same thing, its the sensor in the middle of this picture? If so, it has a seperate harness and will need to be hooked up or you will not have 4wd. This wire engages your front axle actuator. By shifting the transfer case your engaging the driveshaft, but it will only free spin.
http://coloradok5.com/photos/data/500/P1090005.JPG

All of this is assuming your still running the 94 ifs and np241 that came in the 94 originally

Looks like mine on my '93. The tailshaft sensor is the VSS that goes to the PCM. As depicted above, that sensor shown goes to the floor shift lever.

I left everything original except for hooking up the 4wd Low wire from the PCM. That is something that needs to be done. Since the drivetrain will be spinning at a much slower RPM compared to engine speed in the 4 Low position, the 4 low wire from the PCM must be grounded so the PCM "knows" the drivetrain is in 4 low and shifts the trans accordingly. I mistakenly removed that from my modified original harness and now must repin the PCM and find how I can get the wire grounded in the 4 Low position. It will take some doing but I figured I'd mention it so someone else doesn't make the same mistake I did.

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Originally Posted by slow94

Just to make sure we're talking about the same thing, its the sensor in the middle of this picture? If so, it has a seperate harness and will need to be hooked up or you will not have 4wd. This wire engages your front axle actuator. By shifting the transfer case your engaging the driveshaft, but it will only free spin.
http://coloradok5.com/photos/data/500/P1090005.JPG

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I am pretty sure that is it. It looks a tid bit different. My vss looks like its on the tail shaft of the tcase. Then the 4wd actuator plug ( or whatever you want to call it) is in the middle. I think we are on the right track. So keep the middle plug the way it is. Dont touch it, dont splice into it etcc.....?

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Originally Posted by slow94

All of this is assuming your still running the 94 ifs and np241 that came in the 94 originally

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Correct. 94. IFS. But I switched to a 94 2500 tcase so the splines would match up with my 4l80

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Originally Posted by Mickeymotormount

Looks like mine on my '93. The tailshaft sensor is the VSS that goes to the PCM. As depicted above, that sensor shown goes to the floor shift lever.

I left everything original except for hooking up the 4wd Low wire from the PCM. That is something that needs to be done. Since the drivetrain will be spinning at a much slower RPM compared to engine speed in the 4 Low position, the 4 low wire from the PCM must be grounded so the PCM "knows" the drivetrain is in 4 low and shifts the trans accordingly. I mistakenly removed that from my modified original harness and now must repin the PCM and find how I can get the wire grounded in the 4 Low position. It will take some doing but I figured I'd mention it so someone else doesn't make the same mistake I did.

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Thats really good info. I was having the same problem. Is there any wire specifics you can give me. Routing/ Splicing into what wire? Color of wires? Thanks!

AND since my 94 tcase has a different style vss connector compared to nelsons new style vss pigtail, is that all you do is cut off their pigtail and put the old OBS connector on their harness so it plugs into the tcase? Does it matter what way the wires go?

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Originally Posted by Mickeymotormount

+1 to the above.

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What do you guys think? I have my green speedo wire spliced into the blue wire at the vss buffer box. Do i need to cut the blue wire so its not connected to the buffer box? Here is a pic of how it is.

I think you're hooked to the wrong wire. My '93 truck schematic has the light blue/black wire going to the speedo.The dark blue wire is the Rear Wheel Antilock Brake wire. If you pull the instrument cluster and look at the plug, there are letter designations for all the terminals on the plug. Letter designation "S" should be the light blue/black wire. This wire is the speedo wire. You can either snip it here and run your green wire directly to the plug or snip it at the buffer box being sure to eliminate the buffer box from the circuit.

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Originally Posted by HPICamaroSS

Thats really good info. I was having the same problem. Is there any wire specifics you can give me. Routing/ Splicing into what wire? Color of wires? Thanks!

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Here's the schematics and a description of the operation of the transfer case for a '99 Silverado with the 6.0.. Following years may be the same or different. The 4 wheel drive wire is gray/black and is pinned at the red C-2 connector at location 16. From '03 on, it's the green connector(C-2) and the same gray/black wire at pin #16.

http://i488.photobucket.com/albums/r...s/scan0288.jpg

http://i488.photobucket.com/albums/r...s/scan0289.jpg





Still reviewing my '93 schematics to find out how I can ground this wire when I switch into 4 low. Stay tuned, I may be close to an answer.

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Originally Posted by Mickeymotormount

I think you're hooked to the wrong wire. My '93 truck schematic has the light blue/black wire going to the speedo.The dark blue wire is the Rear Wheel Antilock Brake wire. If you pull the instrument cluster and look at the plug, there are letter designations for all the terminals on the plug. Letter designation "S" should be the light blue/black wire. This wire is the speedo wire. You can either snip it here and run your green wire directly to the plug or snip it at the buffer box being sure to eliminate the buffer box from the circuit.

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Whats weird is the way u see it hooked up in the pic, my speedo worked with my old vss harness connected at the rear transfercase. So I had the green wire spliced to the blue wire, then I had nelsons vss connector for the input, and my obs harness for the vss output....and the symptoms were it didnt want to shift ( obviouisly)....BUT the speedo worked back then. When I hook up nelsons rear vss output on the tcase, the speedo doesnt work.

The way vss is setup in 94, is the twisted pair wires from the vss going straight into that drac box, then the decoded speed signal is fed to the guages, tbi pcm, abs, and cruise. So when you hooked up the old tbi vss wires, you were feeding the guage, but your lq4 pcm did not have a clue how fast you were going causing the weird/no shift.

On the lq4, the vss sensors go straight into the pcm, the pcm decodes the signal based on tire size, gears, etc and then feeds a speed signal to the guages, cruise, abs, etc.

So now that youve hooked up the nelson harness to the transfer case, youre giving the pcm the correct signal it needs to shift, but you've taken the 94 drac box out of the loop by unhooking it. That is where splicing into the blue wire comes in, your bypassing the 94 vss/drac setup and using the speed output from the pcm. Hope that makes sense.

To get the proper ground to the pcm for 4wd low, you can build a simple relay circuit to apply ground when your 1994 transfer case applies 12v.

http://www.the12volt.com/12voltimages/pos2neg.gifhttp://www.the12volt.com/12voltimages/pos2neg.gif

You would hook the 12v output(that went to the tbi pcm) from the transfer case into pin 86, when activated this will apply a ground to pin 87 on the relay, you hook that straight into the lq4 pcm pin 16. Sorry, im on my tablet and its hard to type out long messages.

The light blue goes to the guage.
http://pbr992.photobucket.com/albums...g?t=1375412060

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Originally Posted by slow94

The way vss is setup in 94, is the twisted pair wires from the vss going straight into that drac box, then the decoded speed signal is fed to the guages, tbi pcm, abs, and cruise. So when you hooked up the old tbi vss wires, you were feeding the guage, but your lq4 pcm did not have a clue how fast you were going causing the weird/no shift.

On the lq4, the vss sensors go straight into the pcm, the pcm decodes the signal based on tire size, gears, etc and then feeds a speed signal to the guages, cruise, abs, etc.

So now that youve hooked up the nelson harness to the transfer case, youre giving the pcm the correct signal it needs to shift, but you've taken the 94 drac box out of the loop by unhooking it. That is where splicing into the blue wire comes in, your bypassing the 94 vss/drac setup and using the speed output from the pcm. Hope that makes sense.

To get the proper ground to the pcm for 4wd low, you can build a simple relay circuit to apply ground when your 1994 transfer case applies 12v.

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I did splice into the blue wire. Was that the wrong one in my picture? I spliced into the solid blue. Do I need to splice into the lt blue striped one?

yes, the light blue wire goes to the speedometer, the dark blue feeds something else

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Originally Posted by slow94

yes, the light blue wire goes to the speedometer, the dark blue feeds something else

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When I splice into the light blue wire, do i keep it still connected to the buffer box ( like i did with the dark blue wire in the previous pic), or do i cut it so its not connected to the box. Thanks!

I clipped the wire from the box, and it works fine

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Originally Posted by slow94

I clipped the wire from the box, and it works fine

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Is there a need to hook the solid dark blue wire back up to the box. ( the one that i tapped into the first time)

I believe that dark blue wire went back to the tbi pcm, if you removed the tbi pcm, id just cap that one off

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Originally Posted by slow94

The light blue goes to the guage.
http://pbr992.photobucket.com/albums...g?t=1375412060

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The light blue/black stripe wire goes to your speedometer
The red/white stripe wire goes to your cruise box (if you're using cable throttle, you'll need this hooked up, if drive-by-wire you dontl
Brown c9 is fused power feed for the drac buffer box (just leave alone)
Brown c13 is trans output speed to the tbi pcm (not needed)
Black/white stripe is ground for the drac buffer (just leave alone)
Dark blue goes to the Tbi pcm (not needed)

Purple and green are the vss input wires from the old tbi harness (not needed)

Thats all I can get from my Chiltons.
On my first 94 swap I used a dbw setup and just hooked into the light blue wire. The 94 I'm working on now is a cable throttle, so I spliced the light blue and the red/white wire into the green wire from the lq4 pcm, its not finished yet to tell if cruise will work though.

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Originally Posted by slow94

The light blue/black stripe wire goes to your speedometer
The red/white stripe wire goes to your cruise box (if you're using cable throttle, you'll need this hooked up, if drive-by-wire you dontl
Brown c9 is fused power feed for the drac buffer box (just leave alone)
Brown c13 is trans output speed to the tbi pcm (not needed)
Black/white stripe is ground for the drac buffer (just leave alone)
Dark blue goes to the Tbi pcm (not needed)

Purple and green are the vss input wires from the old tbi harness (not needed)

Thats all I can get from my Chiltons.
On my first 94 swap I used a dbw setup and just hooked into the light blue wire. The 94 I'm working on now is a cable throttle, so I spliced the light blue and the red/white wire into the green wire from the lq4 pcm, its not finished yet to tell if cruise will work though.

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Awesome info, thanks alot. Speedo is working right now ( just way off with my big tires and 4.56 gears) and it is shifting all by itself. Now I just need to figure out if it will shift in 4wd. I got it to go in 4wd in my yard, but didnt want to take it down the road. Thanks for the help!

Just an update for my swap. It only took about 14 months but better late than never.

I had everything hooked up and working except the 4 Low circuit to the PCM. Well, after some testing and lots of research, I simply hooked the dark blue wire from the transfer case switch to the gray/black wire from C-2(Red), position 16 of the PCM. Works like a charm. Turns out the GM wiring diagram for the OBS trucks is wrong where is describes circuit # 1493(dark blue) gets power when the 4 wheel drive is activated. When I disconnected the wire and checked it out, it gets grounded when in the 4 low position. It's open in all the other positions. That's just what the new PCM needs at C-2 position #16 in the 4 low position. After checking a few sites, it turns out that the 4 wheel drive diagram is mistaken.

Figured I'd let others know in case they hit the same stumbling block.

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Originally Posted by Mickeymotormount

Just an update for my swap. It only took about 14 months but better late than never.

I had everything hooked up and working except the 4 Low circuit to the PCM. Well, after some testing and lots of research, I simply hooked the dark blue wire from the transfer case switch to the gray/black wire from C-2(Red), position 16 of the PCM. Works like a charm. Turns out the GM wiring diagram for the OBS trucks is wrong where is describes circuit # 1493(dark blue) gets power when the 4 wheel drive is activated. When I disconnected the wire and checked it out, it gets grounded when in the 4 low position. It's open in all the other positions. That's just what the new PCM needs at C-2 position #16 in the 4 low position. After checking a few sites, it turns out that the 4 wheel drive diagram is mistaken.

Figured I'd let others know in case they hit the same stumbling block.

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Thanks for sharing this...I completed my swap 6 month ago and not finding time to wire my 4 low! I'm very happy to see that the diagram is wrong because I don't want to activate a manual switch to ground and if I can avoid to wire it trough a relay it will be cleaner.