Q: P0705 - 2007 Scion tC

Hello and thanks for contacting YourMechanic. The code P0705 means the transmission range sensor circuit has a fault. This is usually caused by the sensor on the transmission failing. After installing the remote start switch, if you did not hook it into the transmission range selector, then the computer will not know when to start the vehicle. If you hooked up the remove start switch correctly, then the code is saying the there is a communication error between the transmission range sensor and the computer. Check the harness to the sensor for any debris or corrosion. I recommend replacing the transmission range sensor if you have not already changed it. If you changed the sensor already, then check to see if there is power to the plug on the harness to the sensor. Check the ground if there is already power, however, if the there is no power, then trace the wires back to the computer and check the wires on the computer for power. If there is power at the computer, then there is a break in the harness between the computer and the sensor. If there is no power, then check the power and ground to the computer. If the power and ground on the computer is okay, then you would need a new computer.

I recommend back tracking all of the connections that you made when you installed the remote start switch and see if the switch is tied into the computer correctly. If you need assistance with diagnosis, I recommend seeking out a professional to pinpoint the cause of the Check Engine Light code.