Okay, my service engine soon light came on my 93 Dually again but this time it stays on. Took it to Advanced Auto and had it scanned again. It came up with the same two errors as before. Can someone help me figure out what these mean?

Code 59: Transmission Temp Sensor Signal Too High. What does this mean? Would a new sensor fix this? What is high voltage? Does that come from a hot transmission? My transmission seems to get hot fast. I have complained a lot about that on this board.

Code 72: Vehicle Speed Sensor (VSS) Loss of Signal. Is this sensor what also controls the speedometer? I have had no issues with the speedometer. It has never not worked for me. I did buy a new VSS just to replace it. It was 17 bucks for that. Where is the VSS located? I would guess this is by the front tire somewhere?

If someone could give me some more specific information on those two codes, I would greatly appreciate it!

TTT Anyone have any info on these?

Thanks!

Lets see, speedo no work, code says vss signal loss= prolly a bad vss- located in trans/ t-case at rear output, it reads driveshaft speed

As for the trans temp voltage, if your trans is overheating, I would figure that is what is tripping the signal, but if trans is indeed overheating, worry about that first before it burns up

I have had no issues with the speedometer. It has worked fine from the day I got the truck. It has never not worked. I will replace the VSS and see if that fixes the issue.

As for the transmission, I have tried. I have put an auxilary cooler on the front. It is rated for a 40,000 GVW and is intended to be used alone. I am also using the one on the radiator and it still climbs.

Right now with temps in the 20's and 30's, it will actually stay around 130 to 140 which I know is a little low. I would like to see around 180. But if it warms up into even the 40's, the temp just jumps to over 200 very easily. I don't understand it at all. I fluid doesn't smell burnt or is discolored. The transmission only has maybe 10,000 on it max since a over 2 grand rebuild. It doesn't slip into any gear, it doesn't slip when pulling, I have no idea why the dang thing is heating up and no one seems to be able to tell me either.

I'm just wondering if high temps in the transmission cause the high voltage error on readout. When the light came on, the transmission was never above 150.

OK, read it wrong- never NOT worked. If speedo has never failed, not even a glitch, the vss could still be bad. IIRC, it could be getting a break in the signal to computer, constant or momentary. Not positive on this, because some systems feed to computer and computer feeds speedo, on others, there are2 feeds, 1 to computer and seperate to speedo.
On the trans, I would guess that it is sensing excessive heat causing the code. I don't know how to further lower the temp better than what you have done already. Possibly higher line pressure due to performance rebuild causing higher temps?
Good luck

When you have multiple codes it is a good idea to clear the codes and work on the code that gets reset first.

Not knowing what engine your truck has makes it hard to help you.

A code 59 indicates a COLD transmission temp reading NOT HOT. This code can be set by a bad wiring connection or broken wire.

OK, read it wrong- never NOT worked. If speedo has never failed, not even a glitch, the vss could still be bad. IIRC, it could be getting a break in the signal to computer, constant or momentary. Not positive on this, because some systems feed to computer and computer feeds speedo, on others, there are2 feeds, 1 to computer and seperate to speedo.
This wording was not clear to me either.
On a 1993 the VSS signal goes to the “DRAC”. At the DRAC the signal goes separate directions – speedo, computer, cruise, antilock brakes.

Thanks ChevyTech! You are awesome!

Unfortunately, it seems like every time this happens, it is the same two codes. It makes me suspicious.

The light came on about 2 months ago and then went out before I could have it scanned. Pulled the codes and these two came up. Cleared the codes out in case they were old and drove away. Light came on again just before Thanksgiving and stayed on until I could get it scanned. Same exact two codes. I left the store with the light on. (Never cleared the codes) The light did go out after a while and hasn't returned.

The truck has a 454 TBI engine in it. The transmission is a 4L80.

I am wondering on the accuracy of my temp gauge on the transmission. Maybe I am running low temps with my setup but my gauge is wacky. (I will never buy a Cyberdine again. I got one of the expensive digitals and it is junk in my opinion. Way too bright at night and one of the lines is already burnt out and now I am questioning the accuracy. I should of stuck with AutoMeter)

You are welcome. A thank you is always appreciated.

These two items do not share the same connector on the transmission so my next thought is they could share a common ground.

Check the grounds specially the grounds on the top of the engine, which is where the computer related grounds are.

I looked at the schematic for your truck and could not find the ground path for these circuits shown anywhere.

Take advice from chevytech, I have seen severeal of his posts and he seems to know his stuff.
Been a while since I had that body style tbi, but doesn't the wiring all run up by the dist? The reaso I ask is because I once had help installing the trans in my 91 and pinched this harness and it caused all sorts of issues until fixed- later that night.
Also on my 98, the underhood light came loose from the hood and landed on the huge mess of wire next to the dist and melted through the loom and caused many problems, the biggest being a weak ground. The wiring running up the firewall is hard to access, but if damaged will be a PITA.