For several months now my SC has been having an issue downshifting at slower speeds like when turning and heading up the hill in my neighborhood. The transmission acted like it wasn't sure what gear it needed to be in and would shift back and forth in a jerky fashion. Eventually it threw a PO715 code which equates to the Input Turbine Speed Sensor Channel A. I replaced the sensor and the problem was not resolved. I took the car to the dealership who said they were unable to recreate the problem. I spoke with the master technician and he suggested replacing the rear tranny speed sensor as well. I replaced the rear sensor and the problem still did not resolve.

The manual says the next step is either the wiring harness or the ECU. I checked the harness and found no issues. A new ECU through Lexus is around 2600.00. I found a used ECU on Ebay and installed it today. (ECU is a breeze to replace) However, due to the immobilizer, the car would not start of course. Digging around online I found a workaround. Pins 4 and 13 on the OBD are shorted with the ignition switch on for exactly 30 minutes. Turn the switch off, remove the jumper, and voila! Car starts, runs great and shifts perfectly. The ECU cost me 65.00.

 

Very nice. Glad that you got it resolved.

 

What a great bit of info to know! Thanks

 

nice job Helo and you did a GREAT job with this write up!

 

Was it the transmission ECU or the main ECU?

 

Thanks for the kudos BGW! It was the main engine ECU. It controls the shifting by comparing the input and output speed sensors on the transmission. Apparently something had gone wonky in my ECU and it was making it not shift correctly. The engine ECU is on the driver's side of the engine up front near the radiator in a plastic box. The top is held on with 3 10mm bolts. Remove the 3 bolts and take off the lid and you will see the ECU. It 5 connectors on top and 2 brackets that hold the ECU in place. Be sure and remember to unhook the battery if you are removing or replacing it.