Have some more information. I was driving my truck on flat ground i got it up to speed let off the gas and it shifted into overdrive then barley gave it gas and it was still in overdrive but gave it a little more and it kicked out of overdrive. I than drove down a hill at about 50 let off the gas and it stayed in overdrive so i pushed the overdrive off button and it slipped into 3rd. So i know overdrive works. It seems like when the transmission builds hardly any pressure at all it wont stay in overdrive. Is there a pressure switch or sensor that could be out?

thanks

 

How about throttle position?? I am assuming you not working on the 2004.5 and the 1/2 and 2/3 shift are ok.

 

Does transmission temp. have any affect on your shifts? For instance, does it shift into OD when you first start driving on a cold transmission? There is a temp sensor that will CUT OUT the OD of the transmission fluid is over a certain temp. It's pretty high, though. Maybe the temp sensor has malfunctioned?

The shift to OD is governed ONLY by vehicle speed and throttle position. That's why the potentiometer "upgrade" works. It fools the computer into thinking the throttle is at a set position. At least that's my understanding. It's an electric shift accomplished by a solenoid that's controlled by the computer. No pressure sensors involved

So since your OD shift is sort of working, but not working right, I think it's got to be one of the four components. The TPS (or potentiometer if you've got that), the VSS, the temp. sensor, or the computer.

I sure hope I have this right: the shift is accomplished by the computer grounding the orange wire coming from the OD shift solenoid in the transmission. A good way to diagnose if the solenoid is working is to jump a good ground to this orange wire. Install a toggle switch in the cab and see if you can shift in and out of OD this way. Grounded, switch ON, OD should work. Also, make sure you've jumped into the orange wire between the transmission and temp sensor. This way, you'll take the temp sensor out of the equation.

 

Maybe check the wiring of your potentiometer, since it's so simple. I was having very similar problems, so I re-wired carefully the pot before I went through all the other troubleshoots mentioned in your threads. If you still have the plug to the TPS with d-pins going to your pot (like the sticky), check that also. I ended up cutting the plug out and hard wiring. That fixed it.

 

It wont go into overdrive and stay at any temp. But due to it slipping in and out of overdrive the trans temp is higher than normal 185.


I will try hard wiring the poteniometer. Do you think the potentiometer could have gone bad. Ive only had it for about 4 months.

Thanks

 

Sure. That's a real possibility. Or you could have a cruddy connection on the pot or the splice to the wiring. That would make the resistance higher which would raise the shift point.

You can test the pot with a DVM pretty easily. I've found that the old analog style DVMs work better for testing posts. It's easier to watch the needle go up and down than to watch numbers.

 

Mine slipped in a nd out of overdrive for 2 years and finally od is no longer an option... I installed a pot, swapped computers, hard wired overdrive to a switch...nothing... so I figure it is blown out internally... So that might be what ur facing!!

 

Replacing the OD solenoid isn't very hard. You do have to drop the pan and the valve body. But is seems like a few hours well-spent to regain OD. And since you have the valve body off anyway, you can slip in a shift kit and increase the grin factor.

 

I hard wired the potentiometer and grounded the orange/white wire at the overdrive module and still no overdrive.

 

we are in the same boat man!! Truckerdee did mention the od selinoid isn't hard to change... Sounds like you need od a little more than me at the moment, so I would give it a try.... Let us know if it works

 

im going to buy a coolant temp switch and see if that fixes it. Its only a 10$ part. If that doesnt work than i guess im pullin the pan. Why would the tranny shift into overdrive with very little pressure but slip out when i give it gas and it starts building pressure. I wonder if the overdrive unit and solenoid is fine and its just one of the sensors?

 

sometimes when it is really cold the mine will shift into od, but once it warms up a little...bye...bye... So there is a temp switch that also controls od... Man, I thought this truck was supposed to be all mechanical..lol

 

haha me to. well ive done every test to ground out everything and still no overdrive. so i guess im pulling the pan. I just wonder how hard it is to do the od solenoid?

 

The temp sensor works just the opposite. Cold = no lock up, Hot = lock up. I think you have a bad lock up solenoid

 

Is there power at the blue wire?