Dealer says he can't get diagnostic codes...

... until he replaces my 12-volt battery. He got codes that seem to have little to do with my problem, and the service department says they can't get any others 'till there's a good 12-volt in the car. Does that seem right ?

I'll explain:

I park my 2002 Prius (~71,000 miles) on the street, and it's cold here in the winter. Just before leaving for a 3-week vacation, I had to jump the 12-volt. This is the Miata battery I've had in it for 4 years. We arranged to have a neighbor drive it a few times (she says she got to it once per week) while we were gone.

She told us she had to jump the battery to drop it at the airport parking lot for us. When she did so it ran, but gave her a warning light. She was worried about that, so met us at the airport several hours later when our flight came in. Sure enough, we had to jump it. But it ran fine, with no warning lights.

The next morning, I had to jump it again, but the gas engine only ran a few seconds before it shut off and gave me a warning on the display screen that said "Problem". (Three icons on the screen, and the one on the right that the manual calls something like the 'hybrid system' icon was highlighted.)

That was a first for me, so I shut off the car and tried again with the same result. The car would move via the electric propulsion system, but even flooring the pedal wouldn't get the gas engine to start back up. I called a tow truck, and several hours later when he showed up, he wanted me to reposition the Prius for better towing. I had him jump the battery so I could move the car on the electric system and... it ran like a top. I drove to the dealership with the car running as normal.

The dealer says they can't get the gas engine to turn over for more than a few seconds. The guy says they got codes C 0200 and C 0205 (right front and left front wheel speed sensors), but can't get any more codes until there's a good 12-volt battery in it.

I'm pretty sure the 12-volt is dead, so I'll replace it. After reading some threads on the forum and pricing several options I'm going to put in an Optima yellow-top, rather than another Miata battery. I'll do that myself.

But the dealer takes $105 for plugging it into the computer. I can't imagine the battery will be a panacea, nor do I really think the wheel speed sensors are the problem here. Any insights?

Any suggestions for getting the computer to tell us more?

Thanks!

 

So the follow-up question from the n00b is: Why can't the dealer hook up a random 12-volt there in the shop and get whatever codes we need out of the computer? Surely the system isn't so finicky about the battery size that nothing else will work?

Or is it?

 

The update is: The new 12-volt seems to have done the trick.

No difficulties, starting or driving.

We'll institute a family policy of at least one excruciatingly long drive (1 hr +) per month during the winter just to make sure we don't drain the new battery prematurely.

As others have this issue, let me recommend persistence in trying to jump your Prius. I almost never had it work in fewer than three jumps, but eventually a good 12-volt source would start the computer, and the system would run well until the next time I switched the key off. (The exception was that it told me I was averaging 43.1 mpg no matter how efficiently or poorly I drove.)

I trust you'll all forgive me for not returning to the dealer to see if the error codes are gone from the computer. I'm not up for another $105 to have them tell me the new 12-volt isn't spec. The fact that there are no error symbols on the display or warning lights on the dash satisfies my curiosity today.

Thanks for your insights!