Red Triangle and won't restart at lights sometimes and accelerator pedal code

I had a strange problem that I think I figured out. Here's what would happen.

My Gen2 with a rebuilt engine I installed after 250k miles and a fairly recent hybrid battery rebuild would throw a red triangle and go to battery only drive mode SOMETIMES but not always after I sat at a light for a long time or sat in a drive through for a number of minutes waiting on food. When I would go to drive the engine would not restart and the car would go only on battery power. If I pulled over, turned off the car for 10 seconds and then turned it back on it would run and drive normally again. After a while the red triangle would go off.

I went to O'Reilly's and pulled the codes. I have to say that I always have lots of codes. I bought this Prius for $3,000 at 200,000 miles. It has a bad catalytic bank, an abs wheel sensor out, the temp sensor for the thermal tank is out, etc. None of them are issues for me. The car runs fine. The new code was actually the code number for the coolant control valve but it said something about the accelerator pedal position sensor.

OK, so I replaced the coolant control valve because that's a serious problem - if that's what the problem actually is. And I bought a new throttle pedal assembly but didn't have time to install it - and I had to wait 10 days to get it. So I kept driving the car. I drive about 400 miles per day 2 days per week.

The issue NEVER happened while I was actually driving. It ALWAYS happened after sitting for a number of minutes... BUT it didn't ALWAYS happen just because I was sitting. It was very intermittent. However, I did notice that it ONLY HAPPENS when the hybrid battery is down to 2 bars or less (Purple). Strange right?

Final piece of information I live in Texas and it's Summer so my AC is constantly on high.

I surmised from the pattern that is has something to do with the car trying to restart from a low hybrid battery state with all the accessories going at the point of restarting. Again, if I turn the car off and start it BEFORE the AC starts up then it starts fine even after the red triangle.

My conclusion was that the 12 volt battery was weak. So instead of replacing the throttle pedal I replaced the 12 volt battery. I have let the car run with the AC blowing full until the hybrid batter got low and the car restarted fine. I let it keep running without any driving for 30 minutes with multiple engine restarts and no red triangle and everything appears to be working fine.

If something changes I will post. I'm not a mechanic, so maybe someone knows if my assumption is true... but I am thinking that the engine restart with a low hybrid battery uses the 12 volt more, or something like that. I posted this in case someone else has that problem.

 

Thanks. I will look into a code reader. I'm sure the hybrid battery is good. I had a rebuilt one installed less than 2 months ago - from a very good source. I'm less Do it yourself, and more I have a really cheap shadetree mechanic who is really good. I bought a used engine on ebay and he swapped it out for $200 and a couple goats (I live in the country). I'm a huge fan of the GenII Prius. I own two (used to own another one until it was totalled). And my attitude is that there is nothing that can go wrong with one of these cars that I can't fix with ebay, the internet and my shade tree mechanic. PriusChat is by far the best forum I've ever seen.

Just last week my wife's Prius (07) completely died on her while driving on the highway. Completely died. She had it towed. After 10 minutes on here I was 90% sure it was the inverter pump. So I drove 200 miles with nothing more than a fuse in my pocket. I unplugged the inverter pump wires, popped in a new fuse and it started right up. I loaded it on a trailer and brought it home. Tomorrow the new inverter pump will arrive from ebay and I will have my guy install it. There's NO WAY I could have known any of that without this forum. It's the best!

 

I use Windows 10 and have an Iphone, any recommended code reader from amazon? I looked but see a reviews all over the place, most say they don't work with Windows 10, and I'm not sure what I'm looking at. Thanks.

 

Bad news. The red triangle came back when it was sitting with the ac on while I was getting gas and running into the store. So the problem was not the battery. Any ideas?

 

I'm calling it fixed just with the battery. The triangle came on once right after installing the battery, but the flashing one bar gas thing happened then as well. The new battery wasn't fully charged. After it fully charged I have had zero issues with that problem. I've driven the car over 1,000 miles in all conditions. Normally that would have caused at least 4-5 red triangles. I'm calling it fixed.