2000 Windstar will not stay in overdrive

I had the P0171 P0174 CEL. I did the Isolator Bolt fix and that problem seems to be cured. Prior to the doing the isolator bolts I noticed that after about 20 min. of driving the transmission will not stay in over drive. While cruising at a steady 70 mph. the rpms will suddenly increase by about 800 rpms. If I let up on the gas a little I can feel the transmission shift back into overdrive and the rpms drop back to normal. As soon as there is any load on the engine at all, the rpms increase again. I don’t really feel it shift out of overdrive but I can definitely feel it shift back into overdrive when there is no load on the engine. The transmission will stay in overdrive going down hill but on level or up hill sections of road it is running at the higher rpms. When it is running at the higher rpms, if I disengage the overdrive button the rpms stays the same so it would appear that it truly is running in 3rd gear. I have flushed and filled the transmission at 30k 60k and 97k miles using Valvoline synthetic Mercon V at the 60k and 97k changes. I used the procedure called out in the Windstar shop manual. The vehicle now has 104k miles. The problem started before the last transmission fluid change. The fluid change had no effect on the problem. I am thinking possibly the TSS might be the problem but everything works perfectly until the transmission is up to full operating temperature. Even when at full temp the only thing that is affected is overdrive. Any ideas on what this might be?

My transmission shifts down.....you don't feel it...but the RPMs go up suddenly for a second or so when it happens, and then it shifts back up into O/D with a drop in RPMs.
This happens when the A/C compressor engages when I am going up hill, or there is a slight load on the engine.
This is NORMAL operation for when the A/C compressor comes in, as that is a significant increase in engine loading.

Otherwise, it is kind of hard to determine what the correct shift point for the O/D is.
If you are cruising along, and you are at a loading condition, rpm, etc that is close to the downshift point, your transmission can "hunt" between 3rd and 4th gears.
If this condition is happening a lot on a hill, one can press the O/D button to keep the transmission in 3rd for that particular hill.
This is particularly common when towing a trailer, or other higher than normal loading condition.

The transmission will not stay in overdrive even with minimal load. Cruising at 70mph. on level interstate. No AC. No back seat. Driver only. Basiclly an empty vehicle. This only happens after 20min of driving. It holds overdirve very well until the tranmission is at full operating temp. When the problem starts, the only time it will be in overdrive is on down hill sections of road. The rest of the time it is running 3100 rpm at 70mph instead of the normal 2200rpm.

I had a Taurus to do this. The trans pcm had to be reprogram. Not sure in your case.. I thought it was the TRS but it was not..

garync1, Did your Taurus tranmission throw a code when you had your problem? Who diagnosed the tranmission PCM as the problem?

Unless someone has any new information, I'm going to try the TRS and see if that does any good. I will let everyone know the results.

garync1, Did your Taurus tranmission throw a code when you had your problem? Who diagnosed the tranmission PCM as the problem?
NO code.. It was still under warranty at the time.. But you can test your range sensor by disconnecting it first. You will need to have the van running. Or it wont start. I did this test before just to see how it works. Just drive normal don't try to pass anyone or have a heavy foot on the gas. If no change happens then most likely its not the trs..You will have to remove some of the air intake tube to get to this part. Just make sure you hook it back up. I left mine a little loose to make for quick hook up after test was done..

I Have A 98 Windstar, And I Had My Trans Replaced By The Dealer While I Still Had A Little Warranty Left. The First Trans Had A Slip From First To Second At 70,000 Miles, But This One At 100,000 Miles Has The Same Problem You Are Talking About, But The Overdrive Light On The Shifter Handle Starts Blinking When There Is An Overload On The Van, And Usually On A Small Incline, After The Temp Gets Up. It Overrevs And Stays There For A Bit Sometimes Longer, Now And Then It Will Do Fine, Not A Problem. But The Light Will Not Stop Blinking Until You Stop And Restart The Van, That Must Reset It, While The Light Is On, If You Come To A Stop And Take Off Again It Shifts Real Hard Into Gear, Again If You Restart The Engine And Reset It, It Shifts Fine. Could This Be The Pcm, Or Something Else, Of Course Gas Mileage Has Taken A Dive.

If your OD light is blinking you can take it in to a dealer or tranmission shop and have the code read. That should lead you to the culprit. My OD light does not blink so I'm still guessing. Haven't had a chance to disconnect the TRS yet to see if that changes things. Maybe tomorrow.

I did some more trouble shooting today. Took the van for a drive until it would no longer stay in overdrive unless letting off the gas or going down hill. I left the van running, unplugged the TRS and headed back out on the road. With the TRS unplugged, the van would not shift into overdrive at all. It acted as if the OD off button was on. I'm not sure what this diagnosis technique is telling me. Any thoughts?

The Windstar is my wife primary vehicle but I've been driving it for the past two days. I have noticed an occasional shudder while the transmission is in overdrive. There is also a shudder just before it shifts out of overdrive. I added Lube Gaurd Red about 400 miles ago but haven't seen any change with the original problem. I'm starting to think this may be terminal. Maybe the pump or pressure regulator.

The only other option is to take to dealer or trans shop. Most of the issues I have seen on here is fluid changes and cooler add on other than that trans problems seem fade away because there hard to find. I think my trans will fail soon maybe but it runs fine except the shudder issue I have every now and again.A trans shop told me it could be the pump but was not sure until it went because I have no codes.Now it has not leaked for a while and don't know why.
May be because its cooling down. I thought the TRS should engage OD while disconnected but not sure on that one. If you find out what the issue is please post because like I said trans issues seem to fade away..Most seem to replace the trans or rebuild or trade in..

I finally broke down and took the windstar into TSI (local tranny shop). They took it for a test drive with a diagnostic tool hooked to the OBDII port. It showed the transmission was indeed shifting into overdrive even though the rpm indicated other wise. They took the tranny apart and found the drum and band for overdrive shot. They are working on getting all the parts for a complete rebuild. I'll let everyone know the rest of their findings when I get the bill. Initial estimate is $1800 out the door. We'll see if they can getter done for that.

The reason the tranny was slipping in overdrive is the servo for OD had worn to the point that fluid was pushing by and not holding enough pressure to keep the band fully engaged. Apparently when the fluid was cold it had enough pressure but as it warmed up it would lose pressure and start to slip. The OD servo on the AX4S is externally mounted. The servo piston passes through the transmission case. The case had actually worn to the point that fluid was leaking by so it could not hold pressure. The shop had to bore the transmission case and install a sleeve in order to salvage the case, otherwise they were looking at a complete replacement. They rebuilt the pump and valves. Replaced the bands and drums and installed a new torque converter. Out the door was $2240. Kind of pricey but hopefully will last for another 100K.

PBZK3,
Did you ever have a flashing OD light or any other indication from the instument panel?

The OD light never flashed. When TSI ran the OBDII diagnostics check it showed everything was working fine. The MCU apparently didn't care that the tach and speedometer were not in a normal range. Normal being 2100rpm at 70mph in overdrive.

>except the shudder issue I have every now and again.

My transmission had a shudder. It would occur primarily in O/D, but also when crusing with the "O/D OFF" button pressed. It was due to a chattering torque converter clutch. When I was crusing on a highway, I would watch the tachometer, and after the RPMs would drop as the clutch engaged, they would go back up during the shudder.