2004 Prius issues after changing 12v battery

Hello,

I just changed my parents 2004 Prius 12v battery after their car stopped while driving accompanied by some error messages on the MFD. I wish I could remember the exact error message, but searching the forums indicated that this is mostly likely caused by a dying/dead 12v battery.

Changing the battery improved things, the car MFD works fine and the car appeared to start fine. I drove it about 500 feet and I got the big red triangle and the car stopped. Fortunately, I was able to get it in neutral and push the car back to their garage.

I noticed that the hybrid battery display indicates only 1 bar! Is it possible that the hybrid battery was drained all the way due to the weak 12v battery? Logically, I thought powering up the car would run the gas engine continuously till the hybrid battery was charged sufficiently, but the engine starts and just turns off after 10 secs. They have plenty of gas in the car. The MFD states "Problem", but that's it!

I went through the diagnostic screen on the MFD and the 12v battery appears to be fine. It reads about 12.5V and when the gas engine is running (for the short 10 sec period), the MFD reads 14.x V.

I apologize if I'm missing something basic, but I've never worked on a Prius before. Is my next step pulling OBD2 codes from this? I don't see an equivalent 'check engine' light besides the "Problem" on the MFD.

Thanks so much for any help. I'm so worn out after today and fell so bad for my parents!

 

Patrick,

Thanks so much for your reply. I'll try out some of your experiments tomorrow when I'm over there again.

 

bisco, I believe they've put less than 60K miles on the car. They don't drive much at all.

Were you guessing the hybrid battery might need to be changed? I was concerned that that would be the problem as well! I believe the hybrid battery warranty is 150K/10 years, so they might be out of luck on duration part!

 

Bisco,

No, I already returned the core. What can be learned from the old battery?

 

Hi Patrick,

Sorry for the late reply. To answer your questions:

1. Yes, there is a red warning icon on the upper left corner of the MFD.

2. No, the Prius is not READY when the gas engine isn't running.

3. Yes, the 14V reading only occurs when the engine is running. The voltage is about 12.7 when engine turns off.

Thanks again.

 

Hello,

So my Dad got a little frustrated and had the car towed to an independent mechanic early this morning before I had a chance to work on it. The good news is that the car is now working! They pulled the codes and indicated that there were quite a few codes coming up. The mechanic said that they had to clean the MAF sensor and the throttle body to get the car to start up and run properly. I guess I don't understand how this would coincide with the 12v battery going out. He said that when the computer resets if the MAF/throttle body is dirty the car might throw up some codes and not start. Does this sound reasonable? This particular mechanic has been pretty good in the past, so I'm inclined to believe it; I just want to understand the theory a bit.

Thanks so much for all the help responses! A Prius might be in my future when my current car dies and things like this make me nervous!

 

Hi JC91006,

Just to be clear, the car did start, it just shutdown within 10 seconds and had the red triangle warning light with the icon on the upper left of the MFD. In fact, I was able to drive the car a short while when I first installed the new battery till it gave me the errors.

Here are the codes the guy pulled:

C0200
C0205
C1241
C1242
C1259
C1310

I'm wondering if I could have just fixed the problem by pulling the negative terminal of the battery a few times. Perhaps the computer got in some confused state when I put in the new battery?