I drive a 1997 Ford Explorer XLT 4X4 with 180,000 miles. A couple months ago my O/D light started flashing. When ever the code flashed i would pull over and I would take the negative cable off to get the codes to clear. While driving it, it would shift normally in till i go to about 40 mph. Then the light would come on and the torque converter would refuse to lock up. I would be in 4th gear at high rpms and when i came to a stop there would be a hard 2-1 shift. I tried solving this by changing the fluid and filter twice. I also replaced the valve body gasket and tcc solenoid. This solved nothing and it continued to do the same thing as before. I then took it to 2 shops. One told me they go the code for the torque converter and that i would need to replace the whole tranny. The next place told me some internal pump was failing and that a rebuild was recommended. After this I continued to drive it knowing there was no point in trying to save the original tranny. My dads best friend owns a shop about an hour away and said he would replace it with a used one for free. All i had to do is pay for parts. Then one day while driving the transmission blew up and i lost all my gears. Then it was taken to my dads best friends shop. While it was there he replaced it with a used one along with a couple other parts like the starter. After the used tranny was put in the same problems still kept happening. They tried clearing the code having no luck. I eventually picked it up my self and took it back home to deal with. I can now get the torque converter to lock up but it doesnt want to till im going over 50mph and at high rpms. The light still comes on when i get to about 40 mphs. I tried clearing the PCM and that fixed nothing. Then i tried replacing the thermostat( It was bad anyways) thinking that the thermostat was not sending the right info to the pcm to make the torque converter lock. Now im completely stuck. I have no idea what could be causing the problem. If anyone else has had this problem and been able to fix it please let me know. I know there are a ton of external sensors that control the torque converter lock up. Any help is appreciated. Thanks!! P.S. sorry about the bad grammer and spelling errors.

 

When they replaced the tranny did they replace the converter too?

 

Yes he did. I think it may be the speed sensor. Going to try and replace it tomorrow.

 

Have you checked sensor outputs? You were headed in the right direction with the thermostat, but it's the sensor that provides the temperature to the ECM/PCM. If the sensor reads in range but low, that could inhibit lockup (if it's like my other Fords). Ford used to have two temp sensors - one for the gauge and one for the computer. The one for the gauge had one wire and the one that went to the computer had two wires.

Other sensor inputs that could affect it (again, assuming it's like my other Fords) are BOO (brake on/off) switch and TPS.

Checking the speed sensor is a good idea. Even if it ohms out OK, you should remove it and see if it's picked up any metal shavings. If so, clean it off.

Keep in mind I'm not telling you to replace the sensors. They should be verified as faulty before replacement.

 

I replaced the sensor for the thermostat that sends the info to the pcm. The thing was cracked in half! Sadly that didn't solve my problem nor did it improve it. I got a new speed sensor too but it didn't want to go in. Probably the wrong size(thanks autozone). Thinking about taking it to Ford down the street to see what they have to say about it.

 

Update. Returned the speed sensor and got a throttle position sensor. Sadly that didn't work either. While letting my truck idle I pushed the throttle in a little and then the engine was stalling. I had to keep pushing the pedal to keep it running. So eventually I just shut it off and restarted it and everything went back to normal(no more stalling). So I was researching the MAF sensor I saw posts about people disconnecting them to see if they worked correctly. So I gave it a try. My engine idled a lot smoother. So I decided to drive with it unplugged to see if it affected my transmission. It did. It was causing the same problems I've been having but made them a lot more noticeable. Going to return the TBS sensor and buy some MAF cleaner and give it a try. I do off road a little and spend a lot of time driving on my buddies farm where a lot of dust gets kicked up.

 

Just a quick note to add to that I did replace my air filter last winter. The one before that was terribly dirty and has seen way better days. Also to add to my transmission symptoms I have noticed a huge loss of power. My accerlation is absolutely terrible. Hopefully cleaning it will be enough and if not then I'm off to the junk yard to find a low mileage one.

 

Today I cleaned the MAF sensor with no luck. Also replaced the fuel filter but that is unrelated to my situation. Still no luck so again I'm back to square 1. I might be overthinking this. It might be the valve body itself. I will have to ask if he reused my old one. I don't think he would but I'll ask anyway. O/D seems to flash once it gets up to temperature or over 45mph. Going to call Fird tomorrow and see how much money they want for me to get a code. Hopefully their scanners will be able to go straight to the source. Who knows we will see.

 

Looking through a 5r55e manual. Says the TFT sensor on the internal wiring harness can cause the transmission to stay in a cold start shift schedule. This causes it to shift sooner and inhabits torque converter lock up. Hmmmm