How many volts should be going into the VSS on the back of a 4L80E

[MuddiGGEr25]

I have 1.10V coming in on the pink wire with black stripe, should there be 5V or 12V? im only getting reverse and 1st gear, and when i let off the throttle at 30mph it just drops back down to idle. im sure if i manually put the trans linkage into L it would hold onto 1st gear, but im trying to get it to shift.

[VileZambonie]

Did you check for DTC's? What is the serial data displaying? Did you check the fuse for VSS buffer? The voltage output from the sensor will vary based on speed output.

On a side note, you haven't provided enough information and if i'm not mistaken you have more than one thread going on which makes it hard to follow exactly what it is you're doing.

[MuddiGGEr25]

Did you check for DTC's? What is the serial data displaying? Did you check the fuse for VSS buffer? The voltage output from the sensor will vary based on speed output.

On a side note, you haven't provided enough information and if i'm not mistaken you have more than one thread going on which makes it hard to follow exactly what it is you're doing.

Its the 1995 454TBI/4L80E that i swapped into the 1988 V20 suburban. I dont have an ALDL port to wire up, nor do i have the check engine light wired up.

Im not talking about voltage output, i was asking about the input voltage, but i traced the wires and they both go directly to the PCM, so im assuming its the correct input from the computer.

I have absolutely no idea where to find the VSS buffer fuse since i got the whole harness and the wires literally go straight from the VSS on the back of the trans (right before the Tcase adapter) up to the PCM

[MuddiGGEr25]

At this point, i am trying to make sure im not missing any connections. the 4L80e does not have a vac line connection that i could see, so im assuming it doesnt have one. its perfectly possible that i did not power one of the + wires or missed a connection. but from what i can tell the TBI/4L80E in 1994/1995 should be able to standalone without any input from the body/original dash

[VileZambonie]

So you have the whole harness but don't have the data link connector or VSS buffer and warning lamps hooked up? It sounds like you need to hook everything up before you start troubleshooting.

Also if it's a 4WD the VSS is on the transfer case not the transmission. I'm not sure what you are probing because the VSS does not send it's signal directly to the ECM. The input speed sensor is on the transmission.

[Irish_Alley]

do these help any?

[Irish_Alley]

and this

[Irish_Alley]

also are you sure its 1st gear and not 2nd? 2nd gear would indicate limp mode. want to say when i did my motor swap without sensors or a computer connected i had 1st and maybe 2nd. we drove it around the farm so i want to say it was second

[MuddiGGEr25]

I just woke up and I'll print off all those papers too and get my CEL connected. I'll just jump the terminals right at the PCM for now just to get the codes. Also I have attached a link that claims the 1991 to 1996 should have theVSS on the drivers rear of the transmission and 1997+ 4wd should have it on the tcase, and I have seen several forums mention the same for 1992 and 1993 in the many searches I have done. That's why I didn't think I had a separate VSS, because the only connector I could find on TCASE that it was attached to was a connector for the 4wd indicator lamp

http://www.novak-adapt.com/knowledge/transmissions/automatic/4l80e

Scroll down to the Speed Sensing section

[Irish_Alley]

you have to think about the 95+ 4x4 is in stock form it should be drivers side drop. my 91 crew cab is passengers side drop so my vss is on the passengers side

[MuddiGGEr25]

Yes this was originally a drivers side drop but im using my NP208 so passenger side drop. but i just crawled under and realized the ISS was just coated heavy with di-eletric grease to keep it from rusting (courtesy of the seller) so i then realized the connector i extended was actually for the ISS, so i just wrapped up my "extension" and plugged it into there, and now i have to figure out where the wires are for the OSS on the back top corner of the trans (i am sure its the OSS as its in the location shown in all the pictures for where it should be, and the connector is the same)

I can get a pigtail from the parts store for the OSS monday or tuesday, if they dont have one in the HELP section, but first i need to find out if the "female connector" coming out of the wire loom on the drivers side is supposed to connect to an extension down to the OSS or maybe the transfer case.


I have also read on a couple forums that if i use 4x4lo im going to need to send a signal to the PCM so it shifts correctly?  but i dont have a Speed sensor on the transfer case so i dont know if thats even going to matter, and i dont plan on using it in 4lo anyway




I could theoretically just run a new wire pair up to the PCM to the OSS myself.

(ISS= Input speed sensor)
OSS = Output speed sensor

I can get to 30MPH and its wound out pretty good but not overkill. im gonna hook up the tach tonight or tomorrow and see what RPM im at at 25-30MPH, then i will know for sure what gear im in.


If it helps at all, if anyone has driven a TH400 with the vac line unhooked and you try and drive up to 30ish it doesnt shift and the engine will drop back down to idle if it hasnt grabbed 2nd, thats exactly what it seems like here too

[MuddiGGEr25]

do these help any?

So im looking at pin C15, transmission output speed signal. its a brown wire, single wire, im gonna crawl under there again here later, but i think i saw it earlier, but the speed sensor has 2 wires, just like the input speed sensor ( from what ive been reading, they are both the same physical sensor, the only difference is the location in the transmission.


I wanted to try and manually shift into L, 2, 3 but my shift arm was only long enough to read 3rd gear, so i cant try that unless i put the axle on jack stands since its limited slip, which i might actually give a shot tomorrow, just to see what happens.


I need to find out what color the 2nd wire is for the rear sensor, and i think im just going to run a new set down if i cant figure out which connector its supposed to be

[Irish_Alley]

if you manually put it in 1st you should be able to up shift it

[MuddiGGEr25]

Hey guys, I think I found the pair of wires that is for the rear or output speed sensor after reading a lot if various forums. I am going to try and upload a screenshot of one of them. He said he has been using it like this for a while now and no issues. 


From what I can tell from my research, up until a certain year, seemingly 1996 when they switched to obd2, there were 3 speed sensors: input speed sensor towards the front, output speed sensor to the rear, and a vehicle speed sensor on the transfer case on 4x4 models to let the computer know when it was in 4lo to change to a different mapping table. 4l60e omitted the input speed sensor from what I have gathered from people doing swaps.   The ISS and OSS both go to the TCM or in my case the PCM the vehicle speed sensor on the tcase (4x4 only) goes up to the DRAC and buffer and gets converted for the speedometer and cruise control. Since I am using neither of those for now I won't be needing the buffer or 3rd speed sensor.

I am going to have the local parts store request one of the pigtails today and I'll be putting it on Friday and see if it will shift correctly.

My backup plan is to extend my spare shift linkage arm from a 4l60e by about 3" and put it in there so I can manually up shift if my pcm won't shift with the 2 speed sensors

[MuddiGGEr25]

Here are the screen shots from one of the forums