Car died. Codes make no sense. ECU or 12v Batt?

How low do you think the voltage needs to drop before the ECU will start malfunctioning (actually malfunctioning, that is, not just producing codes you assume are nonsensical to save the effort of making sense of them)?

Is there someone on PriusChat who might have happened to open some of the ECUs to see if they use 5 volt or 3.3 volt logic chips (or some other voltage)?

The only data points I can contribute are that for two Prii that I've owned, and several low-battery incidents down to 7 volts or so, ECUs have not produced any codes that didn't mean exactly what the manual said they mean.

-Chap

 

Two things are wrong with that question:
How LONG the voltage drops doesn't matter; what it drops TO does.
Producing invalid failure codes is an actual malfunction.

I don't know the actual value. Seems like I remember a couple of owners having multiple unrelated codes show up when the battery voltage got down around 10.

 

I'd be the first to agree, were I to see it happen.

I remember seeing even more than a couple such posts on PriusChat, in the nine years I've been reading. The trouble is, in every such post I've seen, the claim "these codes are unrelated/invalid/nonsensical, therefore an ECU malfunction" is made as an alternative to looking them up and reasoning out how they might be causally related, not as a conclusion supported by having actually done so.

It's not uncommon for such posts to be fairly diagnosable even from afar, just using the manual and its information on exactly what triggers the supposedly nonsense codes.

If you prophesy that you won't find out what your codes are telling you, and you act on your prophecy by not finding out, your prophecy is right every time. It just doesn't tell you anything about the car.

This could stay at the level of a wry "people are funny" observation, but I really wince every time I see somebody come on to PriusChat with an actual problem with their car, get their wallet lightened and solution of the problem delayed by being advised to ignore the most direct evidence they have of what the problem is, detour through battery replacement (which incidentally erases that evidence), feel that initial elation of "hey that fixed it" because the codes were erased, and then some variable time later, either in the same thread or a new one, come back with some oddly familiar problem, now feeling like their car is nothing but trouble and some kind of problem magnet.

-Chap

 

he said "How low" and not How LONG, go ahead and reread it a few times.
your blaming every possible prius problem on bad 12V battery is really getting old (no pun intended).

 

And yet you seem perfectly happy to completely ignore those who have an 8 year old battery or one that reads 10 volts and starts throwing multiple codes suddenly..........AND come back weeks or months later to report that a new battery made the problem completely go away.
Why is that ??

IF......the battery tests good AND there is no other reason to suspect it, then maybe digging into the codes is a good idea......maybe.

The problem with that IS that most who come here asking for advice have no access to good information on the codes AND they have no experience to recognize how the codes could be tied to other symptoms. If they had that skill or knowledge they wouldn't be asking in the first place.

I think that blindly diving into "analyzing" the codes without first taking about the common power supply is doing folks a dis-service; sometimes BIG TIME.

 

Sorry I did mis-read that.

But your second statement is grossly unfair and inaccurate too.
You don't like my advice......ignore it.......or prove me wrong.

 

I need to share this... note this is based on a different car, a 2006 Volvo V50.

I have a work colleague who drives the above car and he was made to change the starter motor ($3000) in 2014 when he experienced engine issue. 1 year or so later, the car's cruise control stopped working, and the engine idles at crazy RPM when it first started from cold. The dealer said it was the ECM, which will cost another $2000 to replace. He wasn't going to spend that money, so he ordered the ECM from a wrecker in the US to try to resolve the issue. Volvo charged him $1200 just to replace the ECM and fault diagnosis... it was 6 months mucking about to no avail. Meanwhile, I was in the process to changing the Prius 12V battery because it would have been 7 years, and I want it changed even though it was still OK from the load test. I told him he should have it changed given his 12V battery was still from 2006... Guess what, all his car problems (cruise control, idling at cold) went away magically after a battery change. We are in the believe that his starter motor was probably OK. All these times Volvo never mentioned a word about the 12V being the cause, it was a matter of luck that I was telling him about the change of 12V in the Prius. In summary, don't just trust what your mechanic said, especially ones from the stealership.

 

I wasn't going to reply again but now feel the need to explain just a bit.

It is about good troubleshooting procedure.......which none of the tech schools seem to teach these days.

Good procedure is to find out, by whatever means, ALL of the possible things that could cause the problem(s) at hand.
Then if one or two of possible fixes are cheap and easy, as in 1/4 the cost of the other possible fixes, then you should do them first......not last.

Of course some testing would be nice to try and verify what really IS causing the problem but there isn't always a good test.

In the case of a possibly bad battery, it is almost criminal NOT to try a new one before you take a wild guess at another part which costs over a thousand dollars.

 

Thanks for coming back with feedback. Do the codes make sense now? For the record, I suggested EGR in the post #13, unlike some other members who argued hard it had to be 12v problem.

 

Just stop with the insults please.
NOBODY said that it HAD to be a 12 V problem, ever.

AND.......did you not notice that he said the 12 V battery WAS going bad ??

Or do you just enjoy stirring up crap.

 

Battery didn't create the misfiring codes.

 

done