Torque Converter Circuit Electrical Problem code P0743
 

My torque converter stays locked up when I come to a stop or slow down, which causes the car to stall and cut off. It happens occasionally and if I'm really careful driving (coming to stop slowly allowing the tranny to shift down and the torque converter to disengage, it will idle fine at a stop). So the trouble code is P0743 which is the Torque Converter Electrical Circuit, which I have gathered keeps the converter locked on if there is a short or if its grounded (not sure which).

My question is how does one go about changing this circuit? I have not been able to find any diagrams anywhere about the electrical components to these transmissions. Could it be a solenoid? Any help is greatly appreciated by anyone that has had this problem before? Thanks.

1997 Expedition XLT 5.4L, and all fuses are good, recently changed the EGR Tube, IAC, and PCV valves. Transmission fluid is good too.

If you plug your fault code into the SEARCH engine, you'll find 60 posts that mention it. Your answer is likely there.

Believe it or not I actually did that before asking. Plugged my fault code into the search engine in the Expedition & Navigator forum and there are only 5 posts (2 of which show up because the posts have a list and description of all fault codes), so make it 3 posts, Of those 3 posts, 1 is from August 2007 and never even got a response, of the other 2 there are responses and but no resolutions to the problems other than to say "Yep, its an electrical problem", I figured I'd ask a detailed question and maybe I'd get a detailed answer. Thanks anyways.

Thanks I've done that too, and I will need lots of luck because no one even begins to give any relevant answers beyond what I have troubleshooted myself in the garage. I already know what the code means and that its an electrical problem related to a short to ground or solenoid malfunction, so thats why I was asking because my question wasn't answered elsewhere.

If anyone has resolved this problem before, your insight would be more than welcome and appreciated.

Upon further investigation, I have found out that I have an E40D transmission, so I figured I would just replace the torque converter clutch solenoid, but my local Ford dealer doesn't even list a tcc solenoid for my transmission, only for the 4R70W and some other transmission? Is there a difference in tcc solenoids between the E40D/4R100/4R70W transmissions?

The E40D & 4R100 have a shift control unit or solenoid pack...whatever you want to call it. It has all the solenoids together so you replace the whole pack. 4R70W & that style unit have individual solenoids.
To replace the pack you have to drop the trans pan. If you find a lot of metal fragments in the pan/on the magnet then don't even bother changing the solenoids...you have internal failure. A lot of times the solenoids will get clogged with metal & trip a code.

I have a transmission shop on Long Island...if you live anywhere close I could check it for you.

Thanks, I'm going to order the solenoid and check out the conditions inside the pan. The transmission shifts fine so I'm hoping this will solve my problem. As of late the problem has decreased, the idle will drop when coming to a stop but its still been strong enough to overcome the torque converter and keep the vehicle and will idle as normal at a stop in gear.

Are the PWM and Non-PWM solenoid packs for the E40D transmission interchangeable? I really don't know if my tranny is PWM or not.

If I only lived in Long Island, instead of Rochester NY, I'd take it to you :)

It is highly recommended that you follow the pinpoint diagnostic in the Workshop manual instead of guessing.

The fault might be a wiring harness fault, a faulty PCM, or a faulty solenoid/pack in the transmission.

If you just throw parts at it and hope to get lucky, you are going to be sorely disappointed.

Where does one find the Workshop manual? Is it available online or is it a book that can be bought? What is the actual title of the manual so I can search for it?

Update: Since ordering a replacement solenoid pack (I haven't received it in the mail yet) my expy isn't stalling at stops anymore and is driving normal. Maybe it was actually the IAC that was keeping the car from idling high enough to overcome the torque converter???

Is it worth it to install the replacement solenoid pack since I've already paid for it or just leave well enough alone?

projectSHO89 - I'm still interested in reading the workshop manual if you can point me in the right direction.

marco,

you can find the manuals on ebay. I'd search for "ford service CD" or "ford service dvd"

projectSHO89,

Thank you for your help, I found the ford service information DVD, and put it to work. Unfortunately I don't have all the diagnostic tools that it called for in troubleshooting the torque converter electrical problem, but the diagrams were helpful in allowing me to see the wiring for the pcm and tcc solenoid. I pulled the pcm and checked the pins for a ground by using my homemade testlight (regular car accessory light with 2 wires), I put one wire in the pin 54 for torque converter solenoid and the other to the positive battery terminal and the light came on, indicating there was a short to ground (just as the symptoms suggested). I followed the wiring harness until I came to a section on the passenger side just above the exhaust manifold that had melted through.

With all the wires exposed and touching was creating a short to ground, so after a little electrical tape and a couple inches of replacement wire, the truck runs 100% correct.

And you were right, I would have been disappointed if I kept throwing parts at it. I realized that after I put in a rebuilt solenoid and the same problem existed (my original was probably wasn't bad after all), but at least I didn't lose out by getting a new torque converter.

To anyone else having these type of problems, I suggest checking the wiring before replacing any parts.

Great feedback in identifying the fault and the resolution!

Glad you stuck to it and saved hundreds , if not more, of dollars by repairing it yourself.

As part of that resolution I forgot to mention that because of the location of the wiring in close proximity to the engine and exhaust, I shielded the portion of the wires that would be near the exhaust manifold and engine with the fire proof sheathing that came from my old EGR tube (I'm glad I didn't throw it out) and held it in place with ordinary hose clamps. This is just to prevent the same problem from reoccuring. There was some heat protection on the that section of the wiring tube but it had given out.

If you don't have such a sheathing, find something heat resistant/fireproof to protect the wiring. You'll also have to disconnect the 5 connections above and around the transmission. The connections go to the Solenoid block, shift selector, exhaust sensor, and 2 more at the end of the tranny, don't know what they're called. Be sure to tie a string around the 2 connections as the end of the tranny to make it easier to feed/pull the wire back into place after any repairs have been made.

Tips:
Remove the passenger side heat shield (the hardest part of the job) to allow for access.
Remove front passenger side wheel to allow some access through the wheel well.
Pull/Feed the wiring back into the engine compartment, but don't force anything.
While you have have electrical connections exposed, inspect and clean any corrosion.