Hey all, I'm new to the forum so I apologize if this subject has been covered before. I have a transmission problem with my 2001 Expedition and was hoping someone out there can provide some insight.

The vehicle is the XLT package, 5.4 motor, 4x4 and 4R100 transmission. My problem began when I noticed an occasional hard shift while going up through the gears. First it wa subtle making me think I may have hit a bump while shifting but it soon became apparent it was slamming into gear. It also would at times moving from park to drive, act like a slipping clutch. Not much forward momentum despite a rise in rpm.

The trans fluid was full and did not smell burnt or look dis colored. I should mention here I bought the vehicle used with 70k miles on it and have no idea if the trans has ever been serviced. Problems only got worse. I would drive a few miles and the vehicle would shift up and down through the gears when it shouldn't and then for lack of a better description, it sounded and felt like the front axle was engaging (AWD kicking in) for no reason.

I rented a diagnostic tool from the local parts store and the vehicle displayed a P0715 error code. I have read so much on this code from so many different sources I am beginning to believe the code could mean almost anything, but the guys at the parts store advise me of the speed sensors on the transmission. So I buy one (I know it has two) and replaced it with no effect. I then took the new one out and put it in place of the second sensor, again no effect. I have checked all the electrical connections I can find and they all look really clean and unaltered.

I then hen take it to the dealer (after I cleared the code) and have them look at it. I spoke with the mechanic after a few days of them poking around with it and the only thing he can offer is a $5000.00 replacement transmission. He could not tell me exactly what was wrong but said with his checking the vehicle he believes the problem is in the transmission and not outside of it. He was miffed I had cleared the codes because no the vehicle will not show the code again no matter how much you drive it or how badly it performs. He did hint to me if I were to repair it myself, he would look at the solenoid shift pack.

Thinking I was armed with a cheap solution I took the old girl home and changed the fluid/filter and replaced the solenoid pack with a rebuilt. As my luck would have it, it runs no better. I should also mention I was a little disappointed with the amount of crud in the bottom of transmission pan which I thought was excessive.

I can buy a rebuilt transmission with a decent warranty for $1600 and am thinking about doing this. The mechanical work is well within my abilities, but the possible electrical/computer issues is where I get lost. So I ask if anyone out there has a suggestion, something I may have overlooked before I buy a transmission I may not need?

 

That right there could be the telltale sign of what's wrong...the clutches are burnt up.

 

I forgot to mention an important part. The vehicle acts fine until it is warmed up.

 

The code indicates an electrical circuit problem with the turbine speed sensor, which is the speed sensor on the top, front of the transmission. Since you put a new one in and it didn't fix it I can tell you that I'm now 99% sure that the problem is in the wiring between the PCM and the turbine speed sensor. Just because the connections look good doesn't mean the wiring is intact. The problem is often in the wiring away from a connector. I recommend doing an electrical continuity check between the PCM and the speed sensor connector. Check for open circuit, short to ground, or short to power.

You didn't talk to a mechanic, you talked to a parts changer. The difference is that a mechanic diagnoses what's wrong and a parts changer just takes random guesses and changes parts, hoping to get lucky. The part about a transmission never setting the code again? That is totally untrue. This proves that the parts changer has no idea about how this works, so of course he can't diagnose the problem. He can only change parts, such as the solenoid body, which would be very low on my guess list.

You've overlooked the P0715 code. I believe the wiring is your problem.

 

I will check this, thank you for the reply.