Robertcave

Your Alternator is duff it should be charging at 14.4 if its only 13.6 as you are driving with youe electical stuff on that will quickly go below 12 therefore you will have flat battery
your Alternator is duff or your belt is slipping

bclexus

When a diode fails in an alternator the alternator delivers waves of AC voltage instead of rectified pure DC voltage. That condition will cause the battery to fail.

The owner has a VOM necessary to check the DC voltage. He needs to check to see if the voltage coming from the alternator has any indication of AC (indicating a failed diode). It's just a matter of putting the VOM on 'AC Voltage' to check it.

krawfo

Battery voltage 9.0 this a.m. after sitting in the garage for 24 hrs but car started right up. I'm shocked. Unfortunately my multimeter is auto-ranging so I'm unable to measure AC voltage. I checked to make sure the trunk light isn't on - no joy. I may have to take it in and have them run the test mentioned in the TSB.

peteharvey

You must set your multimeter to DC voltage, as opposed to AC voltage.

However, most likely your alternator is malfunctioning.

bclexus

The OP does need to check to see if his alternator is delivering any trace of AC voltage, which happens when a bridge rectifier diode inside the alternator fails. The alternator's diode string rectifies AC voltage to pure DC voltage. An alternator that delivers waves or traces of AC voltage to the battery will cause the battery to fail very quickly.

Knucklebus

Wouldn't a failed diode fail open not closed?

bclexus

A bad or failed diode in an alternator is not necessarily an open diode, but more than likely a leaky or shorted diode, which will deliver an AC ripple voltage instead of a full wave bridge pure DC voltage. This 'ripple' is a rather small amount of AC voltage piggybacking on the DC voltage - in essence both DC and AC at the same time. It doesn't take much to damage some sensitive electronic equipment and kill batteries...

I believe the OP said his VOM was auto-ranging, which will automatically detect and display DC voltage which is what the alternator is primarily putting out, but such a auto-ranging VOM likely prevents him from selecting dedicated AC voltage which he needs to read so he can find out if he has more than .50 volts of AC output from his alternator which causes a ripple on the output voltage and can damage electronics and drastically shorten the life of a battery.

krawfo

Thanks everyone for your comments. I borrowed another meter and measured .016 - .018 VAC with engine running so I assume this means the alternator is ok.

bclexus

Yes, that indicates your alternator is working correctly.

jgscott

iTrader: (1)

Why don't you just go some where and let them do a check including a load test?

peteharvey

There's more to the alternator than that.
You are only getting 13.6 V DC, when you should really be getting 14.4 V DC?
I would take it to a mechanic to have it checked out.
About a year ago, my old ES was getting 13.6 V and I thought it was fine [just like you], but Toyota told me it was faulty; they replaced the alternator, and everything has been great since.

jgscott

iTrader: (1)

That's why I said he should got get a complete charging system battery test. Something is being missed.

bclexus

It depends...it depends on the alternator, the loads being energized during the test and the battery itself. 13.6 volts as tested at the battery terminals with the engine idling relatively high enough and some loads energized is typically okay. Others may test at 14 volts or upwards close to even 15 volts.

If the alternator is not making a whining noise (indicating failing diodes) and there is virtually no AC voltage on the output (indicating no diode failure) most of the time the culprit of a battery dying again and again is the battery itself. Oftentimes the problem with such a battery is a shorted cell. A practically brand new battery can have a shorted cell. Just because a battery was recently replaced and not very old does not mean the battery can't fail, especially when the battery is found to have a shorted cell, which is very common...

The OP should take his car to his Lexus dealer or a local National Tire & Battery (NTB) store or most any auto parts store like O'Reilly Auto Parts, AutoZone, Pep Boys, etc. to have the battery load tested as a courtesy at no charge. It takes all of 3 to 5 minutes and can be done in the parking lot as you wait and watch. Most places will even give you the data printout sheet from the load test.

The last thing anyone wants is a battery that won't start their vehicle, or a battery that can't be trusted because it will usually strand you at the most inopportune time. Having a good battery is extremely important - they aren't all that expensive if you amortize the cost over how long a typical battery usually lasts. There really is no excuse not having the battery load tested once every other year after a battery gets to be two years old. Even replacing a battery every 5-7 years before it fails is a reasonable habit - because they aren't all that expensive. However, some people will see how long a battery will last just so they won't have to buy a new battery. In my view, that's not very smart.