Have tried a search to solve the problem, but it seems that in those posts it raised more questions. I have a '92 Chevy 6.5 turbo, 4l80e, I'm assuming its an "E" tranny. less than 90,000 original miles on truck, 4x4, 3/4 ton. K&N filter, hearthrob 4" exhaust.

About a year ago driving home from a short trip, 15 miles or so it wouldn't shift into OD. Talked to a friend of mine with a '99 chevy gas motor said his does the same thing and to just shut off motor and restart and it should fix it. Well it did. The problem would happen once every 3 months or so, simply turn off motor and problem solved. Over the past couple weeks it has gotten worse until today OD won't work at all. Truck is only driven on weekends and the past two days because my work car is broke.

It had almost gotten to the point I could tell when OD wasn't going to work. Nicely rolling on the throttle from a dead stop it would shift really really hard from 1st to 2nd gear, when it does a hard shift almost always OD wouldn't work. Today tapping cruise off with the brake peddle for a 40mph zone, coasting for a bit and getting back on throttle, it had no OD. Bump tranny into N, turn off motor while cruising 50 mph and restarting would fix it until the trip home from work (40 miles one way) OD wouldn't work at all, tried probably 6 times turining it off and restarting, let it sit awhile tonight and tried again, no OD. So now the problem is permanent.

While driving 55mph indicator on OD I can shift from D to OD and there is no change in the motor sound nor does it show any signs of shifting.

Have tried unplugging temp sender on radiator and I'm assuming it was the speedo sensor at the back of the transfter case, just unplugged them and plugged them back in. Didn't help.

Any suggestions? If you say to replace or check sensors please be specific on where they are located. Thanks.

I have a 1994 GMC that had the same problem. everything I found was pointing towards the temp. sending unit on the water neck. It was throwing codes for the temp. sending unit, trans. sliping and OD sensor. I went to change the temp. sender and when I unhooked it the wire ends were dirty I cleaned them up and knock on wood I have not had a problem since. I also put straight Stacks out of the bed:D the same time I was messing with the wires but I dont think that fixed it. Try the Temp Sending Unit on the water neck for $15.00 you cant go wrong.

I have had the same problem with mine..but when mine shifts hard 1rst to 2nd overdive always works..when it shifts 1rst to second way to early overdrive doesnt work ..sometimes i can turn it off and everything works great for a lil bit.sometimes it doesnt..eventually it went out completly..and it was TPS..it keeps going out on mine for some reason dunno why

thanks for the reply guys, sounds like very similar problem izyahdaddy. Where is the TPS sensor located? How much was it? Did you replace yours with a GM part?

its located just to the left side of the injector pump..if i'm not mistaking has a green wire and a red wire..very easy to change..no mine was'nt GM..but i would recommend GM the part.thats what i'm doing this time..maybe the ones i have been getting from oriely's are junk..there only$129 and GM is $189

hrc200x are you getting any codes? In the FAQ's 6.5 section there is a good expaination of how to retrieve them.

Would I have codes if the check engine light never comes on? It only comes on to do the bulb check when turning ignition on.

I stopped into the local chevy dealer today and talked to some of the mechanics, they suggested check all grounds, might be a bad ignition switch, kick down cable out of adjustment, loss of 4th gear in tranny (doubt this since it sure seems electrical the way it would work after turning off motor)

izya: did yours loose OD or just lock up?

I can pull the shifter from D to OD and there is no change in RPM.

Would I have codes if the check engine light never comes on? It only comes on to do the bulb check when turning ignition on.

I stopped into the local chevy dealer today and talked to some of the mechanics, they suggested check all grounds, might be a bad ignition switch, kick down cable out of adjustment, loss of 4th gear in tranny (doubt this since it sure seems electrical the way it would work after turning off motor)

izya: did yours loose OD or just lock up?

I can pull the shifter from D to OD and there is no change in RPM.
Sounds like yours is the TPS as stated above. Our trucks only have so many electrically controlled components as opposed to the 94 and up. As for the grounds, you should check them every 6 months or so just to be safe. My TPS went out about 2.5-3 years ago and it was a pain as I was on a trip and had no idea what it was. Easy to change.
As for checking the codes, check the FAQ's as mentioned above but here is a quick snap-shot: Turn key off, get large paperclip and split it in two to make a "U" and place into the "A" & "B" posts of your reader under the dash just left of the steering wheel, turn key to on(but not start) and the check engine light will flash/pulse. You will see "flash", "flash flash" in series of three. If you get different pulses aside from the "1", "2" flashes then count then between flashes and it will then finish out with a series of the "1", "2" again. If just the 1/2 flashes, then you have no codes, if more then you do and read up on them or post them here and they can be found for you.
And yes, you can have codes without the light coming on.
Hope all works out for ya.

Mark

The TPS must Ground. The Transmission and Transmission's computer module must ground, by grounding that component I am talking the negative side of that will ultimately ground. If you have a capacitor that goes between the transmission and the control module it too must ground. When you shut off the truck and run it again it is a history code and not an active code but it returns as an active code I believe. When the transmission will not go into 4th gear the torque converter will not lock up because the computer thinks that the transmission is probably too hot. The Transmission Fluid Temperature sensor should be good to go but check the pin to pin wiring going to and from the sensor. I would blame the connections and all grounds dealing with the transmission. Hot mode is primarily an electrical problem that can easlily be repaired,

GenBiltstein: can you tell me exactly where these ground are that should be checked? Where is the tranny temp sensor and the pins that should be cleaned?

Wouldn't it seem safe to say that since this problem started out temporarily a year ago and has now become permanent, that it might be a sensor itself thats bad?

What tells the tranny's to shift hard or not?

hrc 200x GenBiltstein: can you tell me exactly where these ground are that should be checked? Where is the tranny temp sensor and the pins that should be cleaned?
First of all The Temp sensor will not go bad because connections are bad.
Check all grounds pertaining to the tranny as a precaution first.

When you shut off the ignition and turn it back on again you are telling me that you are killing off an historic code and not an active code. There are many reasons why the Transmission's computer stops your transmission from overdrive lockup. Hot Mode. Why? at first glance to me stymies me because if the transmission is running hot then mechanical lockup is what the doctor ordered right?
1. How many miles do you have on your tranny?
2. Is enough air getting through your transmission oil cooler?
3. Have you taken off your transmission connector and cleaned off the electrical connections and made sure that fit and finish is good? after all it is 2007 going into 2008. We have 16 year old sons and daughters that are as old as your truck who are plannong on their proms now!!!
Check your Battery negative, Grounds will also connect to frames so look under your truck. Check from the rear of the Engine block the left and the right heads. each and every ground must be checked.

Where is the transmission control module? I'll check that once I find it.

I was told the same thing by someone else regarding the trans harness where it runs through the case. He said to pull it apart check and clean it. I couldn't figure out how to get the connector off, do I need to drop the pan to do this? I couldn't really see what I was doing and didn't want to force it. I can check the battery grounds and the firewall to head grounds, are there any other grounds to check? Actually I'll probably just replace the ground wires that I can find, she is old enough to deserve new ones.

GenBiltstein, thanks so much for your help, I've been going around and around with this for months, I've had lots of people make suggestions but so far no one has really seemed to know like you do. If you can get me through this I'll buy you a steak dinner!

http://i120.photobucket.com/albums/o187/USMILRET/Transconnection.jpg

Checkthe connection going into the transmission. Check the conector pins going into the transmission.
TFT signal is transmission fluid temperature sensor. The computer receives this signal and determines how thick or thin the fluid is. Too thick and the transmission will not shift. Too thin and the transmission will not go into 4th (OD). Pins L and M are the two pins to check with a multimeter to see if that TFT sensor is working. Check the sensor and you don't have to take out the wiring.
#1 disconnect the connector from the transmission.
#2 locate pins L and M in the connector
#3 with a multimeter and probes to fit from radio shack (I don't know the part #) check for OHMS.
#4 Leave it on OHMS
#5 if you have a 4 wheel drive shift the transfer in neutral and transmission into drive with the engine at about 1200 rpms or so. The Torque converter wil heat the transmission.
#6 the OHMS reading will go down
#7 the Temperature will stabilize around 150-160-170 Farenheit range.
#8 if your TFT sensor is working then the ohms will go down.
I will be posting a TFT OHMS Chart.

Use this chart but remember the temperature should stabilize as stated earlier. You don't have to snap diagnose any longer. If the sensor is working then move to something else. way too many people will try to be helpful but won't know.

http://i120.photobucket.com/albums/o187/USMILRET/TFTSensorOhmsTable.jpg

Take it to a tranny shop. Of course mine did the same thing. 93 GMC 3500, 6.5 with 4L80. Shut it off going down road, starting back would fix it for a while. Check your TPS sensor first (second time mine did this problem it was the TPS sensor). Found out the wiring had gotten fraid inside the transmission causing the OD solenoid to go bad, had to replace solenoid and wiring the first time. Keep tranny fluid changed.

I'm wondering if people are getting torque converter lock up confused with overdrive? Mine will not go into OD, like I said, I can pull the shifter from OD to D and there is no change in shifting or RPM.

How do you disconnect the Multiconnector plug-in your picture? I'm just like detroitdan, I messed with it, but it almost seemed like it wasn't a plug in, From the pic I'm positive it is now, just don't know what I gotta squeeze, pry, or turn to get it apart.

The truck has less than 90,000 original miles.
Radiator (also the tranny cooler) was new a year ago.

lil04fireboy: Was yours not going into OD or not locking up torque converter when the TPS was bad?

If that connector is gray like in the picture then squeeze it from the sides rock it pull gently. Be careful in reconnecting it.

The electronic sub components inside are easy to figure out and hardly go out. 1 and 3 solenoids can be checked with a 9 volt battery the pwm force motor cant because it's too big and a pulse width-variable width solenoid. Hardly goes out anyway. The solenoids are hidden behind the TFT sensor as I have clipped the black zip tie to teach students. You can see the TCC solenoid and the Force motor solenoid at the bottom of the picture. the big solenoid(left is what controls line pressure and the little soneloid (right)controls the TCC clutch). You never have to take the pan off to check connections because you can check them at the main connection with a multimeter. :D

http://i120.photobucket.com/albums/o187/USMILRET/transelectronic.jpg

hrc200x if you simply check for stored codes the trans. maybe telling you what is wrong or at least give a direction were to start looking, it is the first thing you should do, start from there it really easy to do. It's the first thing a GM tech would do.

hrc200x if you simply check for stored codes the trans. maybe telling you what is wrong or at least give a direction were to start looking, it is the first thing you should do, start from there it really easy to do. It's the first thing a GM tech would do
I agree get the codes first. Those pictures are picture to help you understand. In the one picture is a gray sensor sticking up towards the back.

I got the codes, I dont understand how to interpret the flashes, I made a video and can send it to someone. The vid is 6.7mb in size, so high speed would be helpful. Thanks.

Thanks to the phone tech help from GenBiltstein and everyone else, I think the problem is solved. I had to adjust the TPS counter-clockwise just a bit, about a 1/16th inch or so. Drove it probably 10 miles, OD and lockup work fine, no hard shift from 1st to 2nd gear. Checked codes and nothing. Thanks again.

http://i120.photobucket.com/albums/o187/USMILRET/Transconnection.jpg
I finally got that connector off. Is it supposed to be wet? It has trans fluid in it. Tried wiping it out with a clean shop towel but it kept seeping out. Drove it around a little, seemed like lockup worked correctly but sometimes it does anyway. What I did notice is that the speedometer was acting funny. Let off to get off an offramp and the needle climbed a little when it should have dropped. Goosed it and it went down a little rather than up. Seemed to work fine the rest of the way home. This is with a brand new VSS. Not sure if it has done this before and I never noticed, because I almost never look at the speedometer.

Haven't had a chance to try the ohm meter yet.

One other thing, my driveshaft is a little out of balance, has a vibration that's been there for years and I've never bother to correct it. COuld that, in addition to slightly larger tires mess up the VSS?

That connector is not supposed to have any tranny fluid contamination at all. Wreaks havoc it does. Find out why it is seeping. There should be a seal.