working on a 2000 F-150 (5.4L & 4R70W). the truck was towed to me with the complaint it would not go forward.

I found 6 transmission trouble codes set. I cleared the codes and was able to drive the truck for about 30 miles. It shifted perfectly and had all 4 forward gears, codes did not come back. I parked the truck to check the fluid level (it was full) waited about 15 mins and went to move the truck, As soon as I turned the key and started the engine the CEL came on and the OD light started flashing, the transmission would engage in forward gears but would just chatter when you tried to accelerate.

I checked the codes and found P0743, P0750, P0755, P1747 and P1760 set. I tried clearing the codes again several times and come back instantly when the key is turned on.

I doubt all the electrical solenoids in the transmission have failed at the same time. I suspect the internal connector and/or harness maybe faulty. what is the best course of diagnosis on this? where so I start?

 

The solenoids did not all fail at once. The wiring harness did. If you lose the power to the transmission it will set codes for all the solenoids. The first thing I'd check is for power to the transmission connector.

 

Thanks for the response Mark. when you say "wiring harness" are you referring to the black molded harness in the pan? or the external harness outside the transmission that plugs into the bulk head connector?

any ideas what pins I check for power?

 

Here maybe this can help, also check for fluid in the case connector. That will cause this too.

 

thanks JK... there is fluid in the case connector. should I replace it ?

 

Usually it is the outside wiring, not the molded leadframe inside the pan.

 

If the external harness checks out fine then I would look inside and while I was in there I would replace the case connector.

I agree with Mark, I rarely see issues with the internal "hard plastic connector"

 

I found 15 amp fuse #23 in the power distribution box (under the hood) was blown. according to the manual this fuse powers HEGO sensor circuit, Canister Vent, Automatic Transmission and the CMS sensor. Not sure what cause it to blow, yet.

The blown fuse also explains why the CEL came on and codes were stored for canister vent failures.

 

Check the wiring harness that runs down the pass side of the engine and back to the transmission for contact with the exhaust manifold. I have found many with burnt wiring from people not routing the harness correctly. Repair wiring with solder and heat shrink, butt connectors are no good.

 

You were dead on ... transmission harness was mis-routed and wedged between the transmission dipstick and exhaust manifold. Fortunately, I caught in time and only one wire has very slight damage, I should be able to repair it easily.

 

Sweet, glad I could help.