hybrid system warning reappeared after replacing 12V battery

I haven’t been on these boards very often since getting my used 2008 Prius because until now it has been very kind to me in terms of not needing mechanical repairs. Unfortunately that good streak seems to have come to an end. Driving home Monday evening (after ~30min freeway driving), my master system warning light came on, accompanied by the hybrid system warning light. I didn’t know what the latter was – had to look it up – but I immediately pulled to the shoulder. The car was driving normally, however. Since shops and dealers were closed for the evening, after much debate I ended up having the car towed to a family friend’s body shop; they were still there and had a scanner to check the error codes for me. My car was on the side of the freeway for well over an hour with hazard lights on and the dome light on and off occasionally as we got in and out of the car. By the time the tow truck arrived, I discovered that the 12V battery seemed dead; car wouldn’t boot up all the way, wouldn’t shift to neutral and didn’t want to power down – I had to try turning it off upwards of 10 times. I was surprised, given just the hazard light and limited dome light usage. We jumped it, got it in neutral and on the truck.

At the body shop, they said there were no error codes related to the hybrid battery; something about transmission that wasn’t clarified, and errors for low voltage on the 12V battery. With everything off, it measured 10-something V; something higher when turned on, but they believed the problem was a dead 12V battery. I was surprised that it would suddenly give out in the middle of driving, but we went ahead and replaced it the next day. I picked up the car Tues evening, and had no problems driving it home, to work the next morning. Unfortunately, during my drive home – strangely at almost exactly the same location as the first time – the same hybrid system warning light came back on. I’d driving about 70 miles with it off at this point before the reappearance. This time I didn’t pull over to the side (had enough of that before) but rather drove a few more miles to a parking lot where the car has now stayed overnight. I note that the car seemed to drive perfectly normally during that time; no loss of power. Now I need to decide how to proceed and was hoping for some advice. I spend late evening reading several threads here regarding the hybrid warning light but I likely didn’t cover everything.

First, is it possible that the error code just wasn’t cleared properly? Would it automatically clear when they replaced the 12V battery? If not, would it take ~70miles and re-appear?

In my reading on other threads it sounds like another common possibility is the inverter coolant pump. This thread in particular I saw has instructions on checking whether there is turbulence in the inverter fluid bottle. I will look for that when I get down to the car shortly. http://priuschat.com/threads/master-system-warning-light-hybrid-system-warning-light-dealer-says-12v-battery-help.144843/#post-2064136. However, if it were this – would there have been any error codes for the friend to find? Or does that failure cause only the hybrid system warning?

Are there other possibilities likely?

I need to decide whether to take the car to a dealer or a local mechanic shop. I know the dealer will charge a lot just for the diagnostic. My car is at 143k miles so if it were the hybrid battery (I’m in Calif) then I believe it would be covered. But if that isn’t it, if it is something more mundane, then a shop would be my preferred choice for mechanical work. I also need to decide whether to drive it or have it towed at this point.



Any advice would be appreciated!

 

Thanks everyone! I appreciate the feedback and insight. Interesting to learn that different scanners may not be able to see all the codes. I haven't used a scanner before so I didn't realize that. Good to know.

I ended up carefully driving the car to a local shop for a more thorough diagnosis. I don't have my notes with me at the moment, but they did indeed find an error message related to the inverter cooling system, as you all suspected. They were very honest and immediately bought up the recall, suggesting that I call the dealer to see if my car was eligible for the recall replacement. (As the second owner, I didn't know for sure whether it had previously been replaced.) I now have an appointment to take the car into the dealer next week and with luck that will put the issue to rest.

After that is all settled, I think I will take my car back into the shop to have them check out my oil situation. Twice now I've discovered the oil to be suspiciously low; though granted it went a little over schedule on changing it. (currently 11k miles since last change)