voltage...

[dindy]

my friend of mine is worried about some issue with his voltage. he got 1.0 auto 2001 yaris 4 cylinder. on normal idle his voltage is 13.5 but it will increase to 13.7 when rev the engine. when he turns acceseries on, like headlamps , heater blower and hazard lights, it goes down to 12.9 volts on idle, with 13.0 on reving....i noticed too that his battery is on black mark, means it need recharge....think it is from the battery or alternator problem? i almost forgot to say, when he stops on idle u switch on the hazard lights, his car it will go like rev up and down gjust a little bit and the gauge cluster will dimm a bit and bit on again. any answers? thanks and happy holidays.

[CTScott]

It definitely sounds like either the alternator is not working properly and that the car is primarily running off the battery, which is why the battery is now run down as well.

[dindy]

youer sayin that the battery is not chargin cause of alternator not workin good?

[CTScott]

youer sayin that the battery is not chargin cause of alternator not workin good?

Correct

[CoryM]

Chicken or the egg?
A bad battery can draw down on the alternator keeping it from producing full voltage. Charge the battery (or temporarily replace with a known good one) and check your voltage again. Either way you want to have the battery charged because if you replace the alternator, the new one will overwork itself trying to charge the low battery. It is only meant to top-up the battery, not fully charge it. I would guess it is the battery in this case but hard to tell from several thousand km away ;)

Cheers.

[CTScott]

Chicken or the egg?
A bad battery can draw down on the alternator keeping it from producing full voltage. Charge the battery (or temporarily replace with a known good one) and check your voltage again. Either way you want to have the battery charged because if you replace the alternator, the new one will overwork itself trying to charge the low battery. It is only meant to top-up the battery, not fully charge it. I would guess it is the battery in this case but hard to tell from several thousand km away ;)

Cheers.

For the battery to be bad enough to drag down the output of the alternator, it would also not be able to start the engine.

[CoryM]

For the battery to be bad enough to drag down the output of the alternator, it would also not be able to start the engine.

Little car like the Yaris probably draws >100A so there is still a lot of room to start the car, yet draw the voltage down. Also can be that the battery reserve sucks, but still cranks well (for a short time anyhow). I've seen a few misdiagnosed alternators due to batteries. While it is entirely possible to be an alternator, it's far easier/cheaper for the average guy to charge his battery first and see what happens to his voltage. Especially since he should be doing that before putting a new alternator in anyhow.

Cheers.

[CTScott]

Little car like the Yaris probably draws >100A so there is still a lot of room to start the car, yet draw the voltage down. Also can be that the battery reserve sucks, but still cranks well (for a short time anyhow). I've seen a few misdiagnosed alternators due to batteries. While it is entirely possible to be an alternator, it's far easier/cheaper for the average guy to charge his battery first and see what happens to his voltage. Especially since he should be doing that before putting a new alternator in anyhow.

Cheers.

Agreed that the battery should be verified before going through the expense of replacing the alternator.

[dindy]

intresting about the chicken or the egg mate..i like that....yesterday i went to check out his voltage again. got an expensive multimeter to make sure it reads good. so good i tested the battery first, it reads 12.4 volts. then i started the engine. then from the battery termimals, it read 14.0 to 13.9 that for me the alternator hes doing his job. switched the heater on and headlights to bright, no trouble, still 13.9, BUT!! his engine it like shakin a bit, i guess it is normal. he drive up for one week, but battery stays on black indicator, i guess it time for changing it. btw it is 7 years old. anyone knows what voltage should the alternator gives?

[dindy]

btw, i got haynes about yaris, it tells that should be 14.0 volts. but i never depend on this book, i like other people answers.

[CoryM]

Alternator should put out around 14.0V at idle, no load. With how low the Yaris idles, you might see lower though so may want to do testing at slightly higher RPM. I'd say no lower than 13.5V and no higher than 14.5V is normal. The more loads you have on, the less likely the alternator can keep up. If your radiator fans and rear defrost are on, chances are you are running off battery. No way the alternator can keep up to all that current draw. To properly test the charging system you need a "carbon pile load tester", but this isn't something most people own ;) Voltage is only one part. Amperes are just as important.

End of the day I would guess all is working correctly, but at 7yrs old it's probably time to get a new battery in there anyhow.

Cheers.

[CTScott]

intresting about the chicken or the egg mate..i like that....yesterday i went to check out his voltage again. got an expensive multimeter to make sure it reads good. so good i tested the battery first, it reads 12.4 volts. then i started the engine. then from the battery termimals, it read 14.0 to 13.9 that for me the alternator hes doing his job. switched the heater on and headlights to bright, no trouble, still 13.9, BUT!! his engine it like shakin a bit, i guess it is normal. he drive up for one week, but battery stays on black indicator, i guess it time for changing it. btw it is 7 years old. anyone knows what voltage should the alternator gives?

In your initial post you mentioned the voltage dropping down to 12.9 under heavy load. Are you no longer seeing that now that you are using a good volt meter?

[dindy]

thanks for replies. no ct scott. im not seeing 12.9 now....maybe the other volt meter got screw or whatever....tried 2 different volt meters and they read the same 14.0 and 13.8/9 on load.

[CTScott]

thanks for replies. no ct scott. im not seeing 12.9 now....maybe the other volt meter got screw or whatever....tried 2 different volt meters and they read the same 14.0 and 13.8/9 on load.

That is definitely fine. Depending on the brand of battery, seven years is a reasonable life.

[dindy]

magnetic is the brand, and trust me or not, that battery was used so hard for five years. even was on a hyundai accent with 2.0l turbo with 2k sound system...i guest now need to go to junkyard ;)