2008 Toyota Prius No Ready
The customer's complaint was that intermittently the vehicle would not start or "Ready-Up" and none of the dash lights would light up when pressing the start button. The vehicle is equipped with Smart-Key. He also reported a couple of times the vehicle died while driving and would restart after sitting a few hours.
The customer left the vehicle with me for a few days and I was unable to duplicated the concern. I tried all different scenarios to get it to fail: highway driving, stop and go driving, letting the vehicle sit for few hours, idling outside the shop for an hour to no avail. He returned the following week and left it with me again. A few hours after he dropped it off I let it idle for 10 min while I finished another job. When I drove it into my bay and over my in-the-ground lift, the dash went blank and the power steering went tight. Thinking the car was totally dead I went to get out of it and the vehicle lurched forward. Perplexed, I hit the "park" button and pressed the accelerator pedal and the ICE fired up. The wipers, directionals and power windows also did not work.
I first went to the under dash fuse box and checked each fuse with my meter. I found 7 fuses that only had 2.8v. I next reviewed the wiring diagram (attached) and found all 7 fuses were powered by the IGN1 relay. I installed a known good relay (out of my personal Prius) and everything came back to life. I ordered a new one from Toyota and the car was fixed.
The take-aways from this diagnosis were first, it was key that I checked the fuses with my meter. I later went back and checked them with a LED test light and they glowed just as bright as the other properly powered fuses. Next was the fact the vehicle was a hybrid and has electric power steering that was being affected. The vehicle was in idle-stop when it initially failed and seemed to be completely dead. A typical non-hybrid would have stayed running the whole time but the fact that the ICE was off, the dash was dead and it had no power steering, it would have been easy to start going down a much longer/harder diagnostic path.
Another interesting fact: there is a TSB(T-SB-0047-09) that pertains to the IGN1 relay but it reports they fail in sub-zero conditions. It was 70 degrees F the day it finally failed for me.
Hope this helps someone.
I agree with you on the LED test light. Those things can send you down the wrong path when trying to verify proper power. They don't load the circuit so even if it showed good, that doesn't mean it really is good. Always load circuits when testing power and ground.
Nicely done. Thanks for sharing. Personally love working on and reading anything alternative propulsion.