Had the same problem. Took it to the Lexus dealership and took them a week going threw every wire in the car and still lost for answers. I found an old thread that said it was the ground cable connection to the fender has corroided causing the problem. So i gladly relayed the message to the Lexus dealership and low and behold they said that's what they thought it was after testing every single wire in the car and wanting to replace the wiring harness, thank god it was under warranty..