Is the 12v going? Need a 2nd opinion

For cleaning battery posts a small strip of sandpaper is good, maybe the cloth strip kind used for prepping copper pipes for soldering? The name escapes me at the moment.

For the interior of the clamps a spiral bristle brush is good. Again, there's good brushes for prepping copper pipe insides. There is a special automotive combo brush, for both interior and exterior cleaning, but I find sandpaper as good as anything for the posts, and gentler.

Be cognizant: the posts are lead, so clean just as much as needed, try to keep the dust contained, and wash your hands after.

 

The main problem with that approach is that if you don't happen to see it dip very far, you won't convince the "Daisy, Daisy" contingent that you didn't just blink and miss it, or your meter's display responded too slowly.

More reliable to use the 'record' function on the meter:




The faster setting will show what minimum was hit for even 0.001 second. (Though there, you also have to decide how meaningful that is ... with 5 volt microcontrollers fed by on-board regulators and capacitors in each ECU, there'd be a bit of calculation to work out how deep a dip, for how many mS, you would need for the local 5V regulation to falter.)

But yes, more actual observations of that sort would be a real start on the kind of "experience" that so far is missing

from claims like that.

-Chap

 

How about a re-phrase ?
When an amateur observes 12 V or less on his 12 V battery under little to no load......then it is very likely that it will drop significantly BELOW that during the starting process.......and the computer systems onboard won't function properly.

As with a lot of things.......getting the fine details exactly right really isn't important to non-technical folks if the basic advice is sound.

So......when your 12 V battery (really a 12.6 V battery) gets down to 12 or less, it is highly likely that it will soon not function right.
That's all they need to know.

And creating a pissing contest about the fine details does nobody any good.

 

This discussion reminds me of how the nature of DIY sites like this is to help people transition from knowing nothing, to knowing a little bit, to knowing lots... We're all at a different stage in what we know... At the same time people who know more can be a huge help. And the opposite of that are all the comments that are not accurate and no one corrected the inaccuracy in the thread. So not only is there a huge learning process, but there's also a critical thinking process you have to have about comments people make...

 

But it isn't sound, that's the point, and that kind of help non-technical folks don't need.

"Significantly below" can mean lots of things (the beauty of deliberate vagueness, right?), but only one meaning matters here, and that is "so significantly that it's even realistic at all to assume the computers malfunctioned." You're either calling that "very likely" or you're not. If you are, what you call "the fine details" aren't getting through to you.

It would be one thing if that were harmless to others, but it isn't. It ends up encouraging people who have car problems and "no codes" to think "oh, computer malfunction" and not simply realize they used a tool that couldn't read the codes.

It ends up encouraging people who get a code cluster that "doesn't make sense" to think "oh, computer malfunction" and not discover how much it tells you when you follow through to see why it makes sense.

It leads scads of people to spend time and money replacing something that wasn't their problem, in the process erasing what could have helped find their problem, getting a false sense of resolution because of the erasure, leaving the problem unfixed for as long as it takes to cross the warning threshold again, be it minutes or months. (They're luckier if it's minutes, though probably also more ticked off.)

Meanwhile, the thread where they fell in the trap becomes more bait for the next folks.

We can do better for people trying to keep their cars fixed.

-Chap

 

And along these lines... When someone tells someone to get their 12v battery tested at an auto parts store... That's not going to be very helpful because the system for load testing a 12v for a regular car with a regular starter is not going to get the right kind of data? Is that correct? Or is the the data from a load tester at an auto parts store a good enough test?

 

Electronic load testers work fine on any of the common automotive batteries. For my Solar BA5 for example, you select the type, it could be conventional flooded acid, regular AGM, spiral-wound AGM, or Gel.

You also enter spec's CCA (or CA), maybe another option as well.



(Pretty cool: you can take and upload photos to priuschat in one step. Kudos !)

 

Well ... a typical load tester is likely to put a higher load on it than a Prius would ... so it comes down to interpretation. If the load tester passes it, you can be pretty sure it's flying-colors passed for use in a Prius. If the load tester fails it, well, it might keep starting a Prius for a good long time yet, so maybe you just think of it as extra-advance-warning to shop for a replacement.

-Chap

 

^^^ This. ^^^ The creation of the urban legend.

While I exercise considerable restraint in correcting every inaccuracy I see, sometimes it is necessary to push back against the "I read it on the internet" brigade.

And creating a pissing contest throwing out vague generalisations does nobody any good either.

Can I ask, Sam, in regards to the 12 V system, what real data have you collected specific to Prius Gen 2? Have you ever observed what the voltage actually does on a Gen 2? With a good battery? With a bad battery?

I notice your avatar says you have a Prius c, but do you also have a Prius Gen 2 or had one in the past?

 

When someone asks "What time is it ?", they usually don't want or need to hear how to build a watch.
Nor do they want to hear how time is relative.

Keep it real.

 

And I vigorously disagree.

A good technician starts at the most basic point.....and checks the easiest and cheapest things first, especially if some of those things has a history of being problematical in a way that is misleading. (Is it plugged in ? Is the switch turned ON ?)

NOT mentioning that a weak 12 V battery can and often DOES cause you to waste a lot of time and money if you don't make absolutely sure it is NOT the problem FIRST does not do anybody any favors.

Checking the connections and getting a good test on the battery is free or extremely cheap.
Ignoring that and running off on an extended and complicated diatribe on what might be wrong is just not being responsible.......in my opinion.

 

Yes, probably.

If done right, it certainly is a good enough test.
That is, if the test is HELD for more than a few seconds and repeated a couple of times within a few minutes.

It can conclusively tell you if a battery is BAD.
If not done correctly, it might falsely identify one as "good".

AND......like all electronics, a battery can be intermittent too. It can be good one minute and then bad the next.......and then good again.

That is why the recommendation is to just replace it if over 5 years old......because most "technicians" don't understand batteries, even the ones at the dealers.

 

While that seems logical, it is not necessarily true.

The starter in a conventional car needs CURRENT and lots of it.
Sometimes a battery that is getting weak can still supply large currents, for short periods, down to even 10 volts.

Modern electronics requires VOLTAGE with a pretty minimal current requirement.

If the tester in use.......or the person running it......doesn't pay close enough attention to the VOLTAGE during the test they can easily pronounce a battery "good" when it really isn't.

Many MANY posts have been made here in the form "The shop (often a dealer) said my 12 V battery is good. Only to find out later after time and money wasted......that the battery was NOT good and a new one fixed the problem."

 

Makes no difference. A battery is a battery and the electronics in the various models are not that much different, in that they require a certain minimum voltage to operate properly.

You have been around here long enough to have seen the many posts about batteries that "tested good" only to end up being the cause of the original problem.

And I have been an Electronics Engineering Technician for about 50 years.
Good troubleshooting technique is the same no matter what equipment is involved.

I'm done. Taking shots at each other is helping nobody and accomplishing nothing good.

 

Data point:
About 2 years ago, my 2005 was running fine except that the brake pump was taking about 3-5 times longer that normal to make pressure. Assuming that I had one of those recall-worthy devices, I took it to the dealer. They said the pump was fine, didn't find any codes, but the battery was only 8 volts.

But even this data point has fuzzy edges.
Was that 8 volts measured after sitting for a while?
Was it right after the pump ran after sitting a while?
Was it 8.00 volts or 8.xx volts?

All I can conclude from that data is that that particular car has to get pretty low voltage before it'll throw any codes since I had no codes at approximately 8 volts.

 

You're right, if you ask what time it is, someone should look at a clock and tell you. There is no watch-building or fine detail involved.

Now, somebody in the room wants to argue that the clock is "very likely" malfunctioning and the answer is really something different, and wants you to spend your time and money chasing the idea of the clock being wrong while you miss your appointment by ignoring the clock.

It's fair to ask that person to bring some evidence worthy of the amount of your time and money they want you to waste. It's fair to expect that person to understand what relevant evidence would be. Wasting other people's time and money isn't the game to go into for somebody who doesn't want to be asked for supporting evidence.

The clock is saying the OP's car has one or more issues, perhaps minor, perhaps major, that the OP would benefit from finding and fixing. It is not "very likely", or even "likely", that the clock is wrong. Encouraging the OP to think otherwise is a money-wasting, time-wasting, false-hope-raising, problem-prolonging disservice.

Which by now has gone on long enough the problem probably could have been found and fixed twice. We don't even know yet whether it's something expensive and dire or simple and cheap. Worth finding out.

-Chap

Hmm, some posts crossed as I was writing ... just quickly ...

Sure, voltage, typically 5 for the microcontrollers in the ECUs we keep talking about (and also the Vref for their analog sensor circuits), sourced by an on-circuit-board regulator stepping down from the incoming supply.

A regulator does need a bit of headroom to reliably produce its design output. Old linear ones like 7805 needed about two volts and a half, therefore 7.5 in to get stable 5 out. Newer ones, half a volt or less. 5.2 to 5.5 in, rock-solid 5 out.

A watch-building detail? Sure, but it's exactly the kind of detail that our 50 year EET keeps forgetting to test his assumptions against.

Jerry's actual data point fits pretty darned well with what we know about how watches work. And I have several closely matching data points, all in the neighborhood of 7 to 8 volts. Above 7, I could usually start the car, by pulling the brake pump relays first. Below 7, no dice. Never an incorrect trouble code, though, either way.

In Gen 2 and up, I think it's possible to see some codes around 9, because the "transmission control ECU" (the one responsible for parking and unparking) has some codes that actually mean "hey, I'm seeing voltage around 9." Jerry probably didn't get one because the ECU didn't try to unpark until the car was ready, and the voltage was over 13 then.

But anyway, when codes like that are set, they're correct ... they are not signs of computers gone batty.

 

SIGH.
And people will take that statement out of context and remember ONLY this sentence from the whole complicated discussion......and therefore I think it is irresponsible to make that statement........because ALL codes that are set are not "correct", especially when they point to various different (mostly) unrelated systems.

I quit.

 

Haha... When was the last time you ever saw an employee at an auto parts store do something right? Maybe 1 out of 10 times?

 

Actually some people who ask what time it is need alot more waking up to how things work around them then just a simple answer. Long-winded answers to simple questions is what will make Prius Chat great again!

 

There an app for that...