Transmission not shifting into fourth gear/overdrive?

Hello, thanks for using 2CarPros. Has the ECM or the transmission computer been scanned for diagnostic codes yet? This may be a wiring or speed sensor problem. If there are no codes present and the up-shift to fourth is still an issue, then the transmission should be pressure tested by a professional. There are steps to take to determine if the transmission itself or its controller are defective. Let us know if any codes are found, and we can direct you from there.

https://www.2carpros.com/articles/check-engine-light-clear-codes

I just had the scan done by AutoZone and the code is PO744 A/T Servo Valve Solenoid Circuit Malfunction. I have already replaced the solenoid with an OEM part. Note: While I was driving home today and going 65 MPH, I would turn off the overdrive on the gear shift and the RPM at the tachometer will slowly decrease, but when I press the button and turn the overdrive the RPM will drop very quickly at the tachometer to almost zero. I think it is something electric. It might be the speed sensor even if the scan did not show it.

Hello,

This is a circuit code it sounds like one of the wires is broken or not making a good connection. Here is a guide and the engine wiring diagram below to help us get started:

https://www.2carpros.com/articles/how-to-check-wiring

Check out the diagrams (below). Please let us know what happens.

Cheers, Ken

It appears that the wiring diagram is for a Honda. Does that matter?

I updated the images sorry, not sure what happened.

I will try to do some testing of my car's transmission electrical connections. It is going to take me a while to do this. I will let you know what I find out. Thanks!

Please let us know what you find. We are interested to see what it is.

Cheers, Ken

Will do.

Juan