My son has a 2005 Sable with the Vulcan OHV engine and the AX4N transmission.
Recently and very suddenly, the car will not shift into 4th gear and will give the transmission code of P0734 (gear 4 incorrect ratio). However, when the transmission is warm and the car is restarted then it will shift into 4th gear. When it is cold, 1 to 2 and 2 to 3 and then torque converter lockup are very normal. But it won't shift into 4th generally. My son has a long commute and it just stays in 3rd (with the torque converter engaged).
I have the Torque pro app. One of the displays is transmission gear. When cold and not shifting to 4th gear, this display showed "4". So, the car gave the signal to shift to 4th, but it wasn't actually shifting to 4th and was in third gear. If the speed is high enough a transmission warning message comes on with P0734 code (gear 4 incorrect ratio). At that point, the gear display on the torque app shows "3". At this point if I start from stop and progress through the gears, the Torque app transmission display will only go up to "3". Perhaps this is “limp” mode. With the engine and transmission warm, I can turn off the engine completely and restart it and then drive. At this point, it will properly shift to 4th gear. Sometimes there is a hesitation or occasionally an oscillation in rpm when shifting to 4th the first time.
Some background information:
- Car has about 185k miles on it
- The fluid is in good shape and has been changed multiple times (not flushed) about 35k (highway) miles ago. This was done through siphoning, so the filter was not changed. Used Mobil 1 transmission fluid which is compatible with Mercon V.
- The reason the fluid was swapped out was because there was an occasional hard 1-2 shift only when hot. That's why I went with the synthetic fluid. That didn't seem to help the problem, but the transmission has been otherwise performing fine for the last 35k miles
- The transmission was rebuilt when the torque converter was replaced (after failing) about 50k miles ago
- yesterday I replaced the vehicle (or transmission) speed sensor. This apparently helps many who have issues with hard 1-2 shifts. I was hopeful this would help the overdrive issue, but it did not.
Any ideas what this could be? Faulty shift solenoid? Stuck 3-4 accumulator piston? I feel that we are capable of changing out the solenoid successfully, but the effort isn't small and I don't want to do it unless it is likely to be the issue. Is there any way to test a solenoid without having access to it?
Thank you in advance!
Problem is now fixed. We changed out the valve body. We ordered one from ebay for $60. Shifts are great now. I suspect it was the 3-4 shift valve. It took about 6 hours. Hardest part was removing the transmission mount from the frame. Pry bar got generous use for that.
How to remove the transmission cover.
https://www.youtube.com/watch?v=dV0r-mqdrXM
From 5:30 to 9:00 This guy shows how to take off the cover and then remove the valve body.
https://www.youtube.com/watch?v=geQmIrnysNM
Thanks everyone for your input.
Thank you for the update, and hopefully this will help others with similar issues.
Congratulations on fixing a transmission problem!
Make sure that it's just a solenoid. It could be just the solenoid. If that's not the issue, then it's a probably an internal problem with the transmission.
Quick Question: Where did you get this transmission rebuilt at? Have they worked on this car before? If yes, do they specifically work on only Ford transmissions?
Thanks so much for your response! The transmission was rebuilt at a place that is now out of business, unfortunately. It has performed fine over the last 50k miles or so.
Other than removing the valve body cover and applying a voltage to the 3-4 shift solenoid how can I "make sure it's just a solenoid"? The car isn't worth doing a transmission rebuild even at today's used car prices. It is, however, worth me changing out a solenoid, but it would be great to be more certain about that being the problem before I go to the considerable effort of gaining access to the solenoid. In this car the solenoids are not accessible through the transmission pan. The solenoids are located at the end of the transmission. I have to remove engine compartment items and either drop the subframe or remove the transmission mount and raise the transmission in order to gain access.
A higher level scan tool with bi-directional testing should be able to get into the transmission and activate the solenoids on command. Scotty uses an Innova 5160RS for this kind of thing other than his really fancy ones. That's a $350 scan tool.
I'd follow along with @KesterPaul62 and ask where you got the transmission rebuilt. If it was a street corner transmission rebuild joint, there's probably something internal to the transmission that wasn't put together properly, and not just a solenoid. Had this happen with my Vulcan V6 powered 1999 Ford Ranger and after 4 or 5 re-visits for intermittent weird shifts, I chalked it off as a lesson learned, buy a factory remanufactured transmission, don't trust rebuild joints. My initial problem after rebuild was an intermittent hard 1-2 shift when cold and everywhere else fine. They went through 3 valve bodies and the problem went from intermittent when cold to an intermittent, rougher downshift from 2-1 when warm. They tried to say It's a problem with the computer, but it never did it until they touched it. The tranny went 251k on original fluid. It would get hung up in overdrive, but never thudded.
Those Vulcan V6 engines are known to outlast the automatic transmissions they're hooked up to. Too bad Ford didn't design their automatics as well as that engine.
Thanks for your response, as well. Yes, Vulcan V6's last forever and are easy to work on. AX4N transmission's are lousy. Unfortunately, I won't have access to a bi-directional tool.
I guess my son has to decide whether to spend $150 for a well rated transmission shop to diagnose it or whether we attempt to replace the solenoid ourselves. $40 for the solenoid and lots of time for the labor on our part. The former has the advantage of properly diagnosing it (hopefully) so that we don't spend time on something that won't end up helping. The latter has the advantage of saving money which my recent college grad son is trying to do.
I guess knowing a little more about the manner in which solenoids fail would be helpful. Can they partially actuate? Can they be temperature dependent?
I don't know enough about them to say definitively yes or no that being cold can mess with them. With my Ranger, the hard 1-2 shift became less noticeable in the summer time, but came back with a vengeance the following winter. It felt like I was rear ended. I wouldn't even take it to a transmission shop, to be honest. I would find a good general purpose mechanic like Scotty, for lack of a better term, and have them check it out. They won't lie to sell you a transmission job. I've thought about pulling a solenoid in my truck. I only got one back in the box of parts I got back. I demanded they give me my original parts.
Good idea. Many thanks.
You never mentioned changing the filter in the trans. When was that last done? A clogged filter could be partially blocking fluid flow.
Thanks for the reply. I can't say whether the filter was changed when the rebuild was done or not. I don't know. I would assume that they would have. When I changed the fluid after that when I was chasing an occasional hard 1-2 shift, I siphoned the fluid out. I did not change the filter. I was looking online and from what I saw trans oil filters are pretty course and mostly prevent metallic material from circulating and that they rarely get clogged. The only information I saw about transmission oil filters being clogged were from generic what could be wrong with your transmissions from transmission shops as a way of luring people in.
I also heard that when there is a clogged filter that the main symptom is slow engagement from neutral into D or R. Presumably there may be less fluid pressure at low speeds.
Have you actually seen issues with clogged transmission fluid filters? I would be glad for that to be the case given the relative ease of changing it. (The current fluid condition is very nice pink/red color and smells like it did when new.)
My son added Lubeguard over the weekend and drove it to work these past two days on his round trip 100 mile commute. The transmission is no longer no longer shifting into OD. It appears Lubeguard made the situation worse. This is a bit of useful information itself. I suggested Lubeguard as it seems to be used by more transmission shops than Lucas is. It does say it has friction modifiers which seems that the viscosity would be increased. Next step will be to replace the fluid (which was pretty fresh through siphoning replacement 2 years ago) and the filter as was suggested above (which had never been changed). Perhaps the filter is a bit clogged reducing the line pressure and not supplying enough pressure for the OD shift.
My son and I dropped the transmission pan and replaced the filter and the fluid with new Mercon V. No change in the situation. In general before the fluid swap and the Lubegard, it had become more difficult for my son to get the transmission into 4th gear even when it is hot. We can feel it "trying" to make the shift sometimes. Any suggestions as to what to do next? I can get a used valve body for $80 on ebay. I have watched videos and feel confident that we can change it out. Does the valve body comprise all or most of the valves/solenoids that could get stuck and cause this problem? I'd like to have a fairly high degree of certainty that this would fix the problem before attempting the replacement. Again, all responses are welcome. Thank you.
Replace the solenoids and see what happens next.
Thanks. Just as easy to replace the whole valve body as it is to replace the solenoids. Neither is easy on this car as the access to the solenoids is not in the pan like it is in other cars. There are no solenoid codes thrown. Access to the solenoids and valve body is shown in this video. I would like to know of the likelihood that there is an internal valve that could be stuck that is not in the valve body. https://www.youtube.com/watch?v=dV0r-mqdrXM
Really good analysis here: https://www.justanswer.com/ford/7mf2o-ford-freestar-05-ford-freestar-ax4n-transmission.html
From this, it would seem to be likely the 3-4 shift valve in the valve body. Possibly the overdrive servo, but that seems less likely. Opinions welcome.