not starting and check engine light is not coming on.

Were you able to find the problem mine is doing the same thing

having the same issue currently on a 2006 gs300 awd, fans com on high, no ECM communication and the car will not turn over.. can manually activate the starter relay with the ignition on.. but the vehicle will not fire up... currently dianosing and will provide adn update as soon as i come up with an answer.

after 2 days of running diagnostics found the high pressure fuel rail sensor had shorted out and was drawing the 5v ref circuit and stopping most communications from the ecm. disconnect the sensor located on the passenger side fuel rail and the car should fire up... sensor is over 300$ for the part plus labor the sensor has a extended wiring harness that pugs in behind the intake manifold that can be accessed without removal

I have an 06 gs 300 and had the exact same problem and same symptoms as described. it was the fuel pressure sensor which I purchased for 25.00 remanufactured. No need to spend 360.00 for a OEM sensor with a small pigtail connector. I removed the air cleaner assembly, throttle body, plenum and intake manifold to get clear access to the sensor. There really isn't any other way to remove the part. While the intake components were off, you can completely clean the throttle body, all the intake runners and de-carbon all the intake valves. Change the spark plugs as well and you will notice a huge improvement in performance. In a direct injection engine such as in the GS 300, ordinary fuel injection cleaners mixed in with the fuel in the tank will only clean the injectors and the combustion chamber but nothing on the underside of the valves on up to the intake manifold.

Having the same problems