I have a 2005 Toyota Corolla (automatic). The check engine light has been going on and off (and back on) or the last two and a half years. I believe the first time the code was P0741. The transmission was completely rebuilt. It came back on (I believe this time it was P0756) and the torque convertor was replaced. It came on again and the ECM was replaced based on a Toyota recall. It came on again with code P0756, but the shop was not able to figure out why. It went off and on over the next several months and then my transmission went out in December 2014. The entire transmission and torque convertor was replaced (again). Four months later, it has come on again with the same code - P0756. I can't spend any more money and/or time on this car and I'm not expecting the shop to know the reason for this, as they seem to be stumped. Anyone have any insight? Other than the transmission going out, I have not had any major issues with it mechanically. Sometimes the shifting feels a bit off, but nothing major.
Thanks in advance!
With the information I have been looking at and the information you have given me I would have to think that the problem may be in the wire harness.
You had the transmission torque converter replaced for the code PO741 and continued having trouble on and off with the PO756.
The PO756 is a code that is telling the technician that the transmission is not in the gear it is directed to be in because it is having trouble with shift solenoid "B" performance shift valve solenoid S2.
Even with the replacement of the transmission you are still having the PO756 popping up then going out. It sounds like it could be an electrical problem in the wire harness or wire connections related to the transmission.
It is possible that it could be a spot in the harness that has rubbed through to the frame or body causing an intermittent short which may be causing this problem. It could also be a bad body ground going to the engine and or the transmission. Check for loose or corroded connections.
Checking the wiring connector terminals for a good connection can be done by placing a connector terminal of the opposite type into each connector to see if it has a tight connection; it is sometimes called a drag test. If it feels loose going in and out replace the wire connector terminal in the plug connector.
Going to a dealership with the proper diagnostic equipment is also important. There diagnostic scanner can take what is called a snap shot of the data when the transmission is not acting right and they can analyze the problem when it happens by going over the recorded data to locate the malfunction.
There are some other data inputs from the engine that are necessary for proper transmission operation like engine coolant temperature, intake air temperature, engine RPM (crank sensor) and throttle angle sensor. They should also be investigated for proper operation. The gear selector switch for the transmission should also be inspected for proper operation and adjustment.
The ECM/TCM should also be checked for the latest version of software; if it is outdated then it should be updated with the newest version.
I hope this helps you. Get back to me if you have any other questions.