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

[ehjorten]

I may have missed something in the threads, but my 1991 has 3 sensors!!!  First there is an Input Speed Sensor (ISS) on the LH side of the transmission, kind of above the shift linkage.  Second there is an Output Speed Sensor (OSS) that is above the large electrical connector.  Finally, there is the Vehicle Speed Sensor (VSS) that is on the transfer case.  I have no idea what the OSS does, as more modern vehicles do not use it.  Perhaps it is used in our vehicles to tell the difference between low and high range in the transfer case.  More modern vehicles use a simple input from the transfer case to tell when it is in low range.

[MuddiGGEr25]

I may have missed something in the threads, but my 1991 has 3 sensors!!!  First there is an Input Speed Sensor (ISS) on the LH side of the transmission, kind of above the shift linkage.  Second there is an Output Speed Sensor (OSS) that is above the large electrical connector.  Finally, there is the Vehicle Speed Sensor (VSS) that is on the transfer case.  I have no idea what the OSS does, as more modern vehicles do not use it.  Perhaps it is used in our vehicles to tell the difference between low and high range in the transfer case.  More modern vehicles use a simple input from the transfer case to tell when it is in low range.

What I have discovered according to others is the opposite of what you just said. The output speed sensor in conjuction with the input speed sensor let's the transmission Determine shift points and if there is slippage of any components. The VSS like I said before puts out a different signal (DC) and has to go to the buffer before being sent to the PCM or TCM (depending on model) and then also up to the speedometer.

 Modern versions of the 4l80E in 4x4 models omit the output speed sensor and rely on the transfer case signal for both speedometer and shifting.

The tcase sensor on those equipped with 3 sensors only tells the ECM/TCM how to respond when in 4lo. Many people have had 4lo shifting problems but 4hi and 2hi work fine and found out it was the speed sensor on the transfer case. I also read several that could only shift properly in 4lo because the output speed sensor had failed and when shifted to 4lo the computer isn't using the output speed sensor and instead uses the vehicle speed sensor in the tcase and uses a different map in the programming as well.


This ONLY seems to apply to vehicles equipped with the 3 individual sensors on 4x4 4l80E vehicles. 2wd and modern ones omit the OSS

[ehjorten]

Interesting!  I knew there was something funky with the 3 sensors, but didn't know exactly how it interpreted it.  I'm working on a 6.0L LQ4 Conversion on my 1991 V3500, but I am having to cap the OSS electrical connector in my 4L80e and extend the VSS wiring to my transfer case.  Then I will have to figure out some sort of microswitch for the low range signal off of my transfer case linkage or something, as the NP205 doesn't have a switch for that.

[Irish_Alley]

from my memory the sensor that goes to the drac box then to the speedo and ecm is on the output shaft (aka TOSS Transmission output speed sensor). in 4lo the vss takes over, this way if your in 4low your speedo is still reading the correct speed. the way the stock pcm works is the vss (toss) goes to the dracs box from there it changes the pulses from 40 pulses to 2k for the ecm, 4k for cruise control and 128k for abs.

the TISS is mainly for the Torque convector lockup
also check this out
http://www.trucktransdiag.com/downloads/4l80e-tech-info.pdf

[MuddiGGEr25]

All I know is what I have read on various forums. But only seems to be applicable to 1991 to 1995 4l80E 4x4 bUT not all of them. 


If the speedo was running off the rear transmisson speed sensor it would be wrong when in 4lo. Think about it. The mechanical speedo runs off the tcase so it's always correct in both hi and lo ranges. It would make more sense for the DRAC, speedo, and cruise control to all run off that sensor on the tcase.

The output shaft of the trans will be turning the same RPM in 4lo or 4hi but the range selected will cause the speed to be either be correct or way off because of the speed of the driveshafts.

 I can also verify that the TISS and TOSS are the same part numbers and put out an AC waveform. I cannot verify that the transfercase puts out a DC signal as I have not tested it. But I do know for a fact it is an entirely different sensor and part number.

Most schematics only show the TISS and the VSs on the tcase with the newer programming and chips

[MuddiGGEr25]

Ok
 Here is a good website for 4l80e pinouts and information 

http://www.michaelrenz.com/4l80e/


I have the DRAC right on my pcm and my pcm says 16197427, but the 2 wires ( dk green with black stripe, purple with white stripe) That would plug into the rear sensor on the transmission are not listed at the PCM on any wiring diagrams but yet I omhed the wires and they go right into the ECM on the red connector at pins  E4 and E7 and E7 is listed as unused.  But the dk green black stripe goes into E7 and purple white stripe goes to E4

[Irish_Alley]

i did leave the important part out about 4lo in my past post. (in 4lo the vss takes over, this way if your in 4low your speedo is still reading the correct speed)
1991 to 1993 four wheel drive trucks use two output speed sensors, one in the rear of the
transmission case, and one in the transfer case. When the transfer case is in 2WD or 4W HI, the
signal from both speed sensors should be the same. The PCM/TCM internal buffer signal is
constantly being compared to the external buffer signal on circuit 437, (Speedometer contained
DRAC on 1991 “K” trucks only). Once the transfer case is shifted to 4W LO, the output shaft speed
sensor signal is now higher than the transfer case output speed sensor. At this time the PCM/TCM
will adjust for shift timing and speedometer accuracy. It is the output shaft speed sensor that is
responsible for shifting the transmission in 2WD and 4W HI. In 4W LO, it is the transfer case output
speed sensor that shifts the transmission, (Refer to Figure 57




1994 to 1995 “K” trucks with 4L80E transmission, eliminated the function of the output shaft
 speed sensor in the rear of the transmission case. However due to engineering problems, the
 speed sensor was left in the hole just to keep oil from spraying out, IT HAD NO FUNCTION
 and no wire connector.
 The speed sensor in the transfer case became the TOSS and the VSS, (Refer to Figure 61).
 Shift timing adjustments and speedometer accuracy in 4W LO range was accomplished
 through the use of a 4WD LO Switch in the transfer case in earlier vehicles and a Transfer
 Case Control Module (TCCM) in the Later 4x4 vehicles. Both 1994 to 1995 “K” and 1993 to
 1994 “T” trucks with 4L60E transmission evolved in a similar way. Beginning with “K” trucks
 in 1996 and “T” trucks in 1995, the “DRAC” was eliminated. All VSS buffering now took
 place inside the Vehicle Control Module (VCM) just like the passenger cars did since the
 4L60E began use in them for the 1994 model year.



http://shop.ukrtrans.biz/wp-content/uploads/catalogs/4L60E_80E_CODE_BOOK.pdf

[Irish_Alley]

might have miss understood the role of the toss. it might just be there to see if the vehicle is in hi or low. if the numbers match the ecm knows its in hi if they dont match the ecm knows its in lo

[Irish_Alley]

· The Input Speed Sensor signal is compared to the Output Speed Sensor, by the computer, to
 calculate gear ratio. A faulty Input Speed Sensor could cause gear ratio error codes to be
 stored.
· The Input Speed Sensor signal is compared to the engine rpm signal, by the computer, to
 calculate TCC slip. A faulty Input Speed Sensor could cause TCC slip codes to be stored.
· Some 4L80E equipped vehicles will have no output RPM displayed on the scan tool when
 there is no input RPM signal. The transmission will react as if it lost the VSS signal, no
 upshift.
· Input Speed Sensor resistance is 1260 to 1540 ohms.

[Irish_Alley]

TOSS & VSS ELECTRICAL VALUE CHART
MPH    AC VOLTS     HERTZ

10            4                   265
20            7                   530
30           10                  800
40           13                  1080
50           15                 1300

[MuddiGGEr25]

I am going to connect to the TOSS because it goes right up to the PCM red connector. And I cannot find an accurate pinout for my truck donor... 1995 K2500 7.4L 4L80E. But I have a DRAC with the letters PYH and the harness didn't have any connections for it, but it's there nonetheless. But I have looked at many many 16197427 PCM wiring diagrams and none of them are correct. There are several pins that are supposed to be not used and I've got wires going into them or not the correct signal accordin to the diagram or the diagram only says 4.3, 5.0 and 5.7 I can't find anything really for the 7.4l. And what I do find is with people with the 13PSI  tbi and I have the 32PSI tbi system so that seems to screw up my luck too

[Irish_Alley]

this is from hatzie
17021.24 GM STG Hydramatic 4L80-E Transmission Electrical Supplement
i cant look at it right now due to a firewall but maybe it can help you out

heres a good list of all the PDFs
http://67-72chevytrucks.com/vboard/showpost.php?p=5621043&postcount=1

[Irish_Alley]

according to that one thing i posted there was no TOSS in 95

[MuddiGGEr25]

Here, I screenshot the pages that had info regarding the TOSS and it's role in shifting. I don't know what year this book is referring to but it says the TOSS is sent to the PCM unbuffered and the tcase sensor is sent to the DRAC. Which would lone up with some of the vehicle combos I have read about. I will know for sure in about an hour or so when I connect the  VOSS and find out if it actually sends a signal to the PCM. I cannot pull it out because I am at a campground and cannot risk to spill ATF.

[MuddiGGEr25]

Quick update. Got the VOSS wired up and it did do a 1st to 2nd shift. I got up to 58mph which should be 3rd but it sounded pretty wound out. But I don't have the tach hooked up till later today