Hello everyone!!



I am trying my hardest to rehabilitate a 2003 Ford Expedition (for reference, it is an XLT Trim with the 5.4L 2V engine and a 4R70W Transmission) for a family friend.



This vehicle was given to my friend and the previous owner stated that the car drives perfectly as long as you make sure to press the button to turn off overdrive before you start driving every time. They had driven the Expedition in this manner for quite some time with absolutely no other issues aside from not having overdrive. Obviously this decreases highway fuel economy on a vehicle that already gulps down the gasoline and is a potential safety risk if you happen to forget to turn off overdrive.



I’ve spent hours and hours looking for any helpful information, but with no success. I have not come across any similar situations on any forum or youtube video. The vehicle shifts and drives flawlessly through gears 1-3 when overdrive is turned off. However, with overdrive in the “normal” on position, it seems to slip into neutral on both the 1-2 and 2-3 shifts. It will eventually shift if you give it a little more gas but only after a couple seconds at higher revs.



When I first took a look at it, the overdrive light was flashing and had two stored codes: P0712 - TFT circuit low voltage input and a P1783 - Transmission over temperature condition. I hooked my scan tool up and verified a bad sensor reading, as it showed extremely erratic fluid temps and would settle at 302° just a few seconds after a cold start.



I dropped the trans pan and replaced the hard plastic molded wiring harness that the fluid temp sensor is integrated into and buttoned everything back up. I made sure to look at the fluid carefully along with the magnet at the bottom of the pan and there were no signs of metal flakes in the fluid or chunks attached to the magnet. Just the normal build up of friction material directly around the magnet. This attempt did successfully take care of the trouble codes which in turn, turned off the flashing overdrive light, but still had no change in shifting ability in regular drive mode.



I did a little more research and saw that there are several things that can cause erratic, or no shift situations including a broken spring in either the 1-2 or 2-3 accumulators and also a possible broken snap ring on the overdrive servo, that can end up dislodging the overdrive servo from the band completely or having a piece of the broken clip get lodged inside the valve body causing shift issues from third to overdrive. I also read that some of the valve body solenoids can go bad and that the rubber check ***** inside the valve body get worn out over time and can also cause problems.



I’m not normally just a parts changer and nothing really matched up with my particular issues since it only acts up if the overdrive is on, but I really was not wanting to drop the pan multiple times and so I just ended up purchasing all the parts mentioned above including a freshly remanufactured valve body with upgraded sonnix shifting components and dug into it again.



As I went through the process of removing and replacing everything, nothing was obviously broken or out of place. I put everything back together, filled it back up with trans fluid and went for a drive.



I’m still having the exact same issues with absolutely no improvement! I need help!! Does anyone have any ideas?



It just makes no sense to me that it will drive so perfectly when overdrive is turned off, but refuses to shift properly in regular drive mode. There are absolutely no DTC codes showing up on the vehicle currently, so I really have no clue where to go from here.



There has to be another faulty sensor somewhere or a wiring harness issue of some kind that is bypassed somehow when overdrive is turned off, or maybe even a miscommunication by the PCM or something, correct?



If there was an actual internal mechanical problem inside the transmission, like worn clutch packs or something, it shouldn’t matter if overdrive is turned off or on. It should just never work properly at all, exhibiting the same symptoms no matter what drive mode you’re currently in, correct?



Thank you for any insights that you might be able to provide!

 

I don't know if you have one already or not but you can download the factory workshop manual here : 2003 Expedition Factory Service Manual Download

It's got some troubleshooting steps in there that might point you in the right direction. Do you have ForScan on a laptop so you can see what commands are being sent to the transmission from the ECM ?

ForScan Software Download ( Free )

 

What happens if you are over 50 MPH and turn on overdrive? Does it shift to overdrive, or does it cause a problem?