Is a voltage output of 13.2 an indication that the alternator needs to be replaced?
Alternator diagnosis (05 Toyota Highlander 3.3L)
- Thread starter Back40
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What issues are you experiencing?
Alt/Batt light on the dash lighting up?
Headlights dimming when you come to a stop?
Or are you just checking the alternator as a PM?
The voltage may drop down to, next-to-nothing or even completely shut down when the engine is completely warmed up/battery fully changed, as to use less power/voltage and only add more voltage to the battery or system apon demand. Yes, systems have always been this way(voltage regulators) but, they are even more efficent today than ever before probably using the computer to control it. I do know that GM's are this way. IDK about Toyota! And, I may not have explained this correctly but others will chime in with the proper answers.
Hope this help a little.
Alt/Batt light on the dash lighting up?
Headlights dimming when you come to a stop?
Or are you just checking the alternator as a PM?
The voltage may drop down to, next-to-nothing or even completely shut down when the engine is completely warmed up/battery fully changed, as to use less power/voltage and only add more voltage to the battery or system apon demand. Yes, systems have always been this way(voltage regulators) but, they are even more efficent today than ever before probably using the computer to control it. I do know that GM's are this way. IDK about Toyota! And, I may not have explained this correctly but others will chime in with the proper answers.
Hope this help a little.
^ good explanation. Volts should go over 13.8 after a cold start; the voltage regulator puts out more when cold to overcome the battery's internal resistance. And they have added computer control in a plot to save .001 MPG.
Also give the motor a rev in case there's cold start smog stuff like catco air pumps taking lots of power. Alts make more above idle... but a base running car without lights etc on should still charge at idle.
Also give the motor a rev in case there's cold start smog stuff like catco air pumps taking lots of power. Alts make more above idle... but a base running car without lights etc on should still charge at idle.
I've seen 13.4-ish after 45 minutes of driving and engine bay hot in at least 1 of my vehicles... it'd be 14.5 when winter cold. This particular vehicle (01 town & country) had a temp sensor in the base of the battery tray.
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IM me if you want the whole doc emailed to you. Really, though, I think you've probably found your problem.
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I think GM even disables the alternator output for a few secs after startup so the idle can stabilize. At least I was told this was the case in my previous Envoy.
This is my daughter's car. She called yesterday and told me the battery was dead after being parked about 3 hrs from returning from the doctor. She had it jumped and said the alternator light in the dash was not illuminated and drove to Autozone where they provided the 13.2 voltage reading and suggested the alternator. I will be heading over tonight with my battery charger and multi-tester. If I confirm the voltage output at 2000 rpm is low 13s then I guess it's time for a rebuilt altenator.
What sucks is it could be a diode or something simple to fix but it is not worth rebuilding them yourself anymore, if you can even find the parts.
Originally Posted By: Back40
She had it jumped and said the alternator light in the dash was not illuminated and drove to Autozone where they provided the 13.2 voltage reading and suggested the alternator.
13.2V out of an alternator that is charging a battery so dead it had to be jumped is not unusual. I would not think there is a problem with the alternator based on that voltage reading alone. You need to know what the load (amps) on the alternator is before you can make a determination as to whether it's bad.
She had it jumped and said the alternator light in the dash was not illuminated and drove to Autozone where they provided the 13.2 voltage reading and suggested the alternator.
13.2V out of an alternator that is charging a battery so dead it had to be jumped is not unusual. I would not think there is a problem with the alternator based on that voltage reading alone. You need to know what the load (amps) on the alternator is before you can make a determination as to whether it's bad.
JHZR2
Staff member
13.2 is a value that might be expected from an alternator. All my diesels put out around there. For a more modern car Id call it weak though.
If it was dead after 3 hours with the alternator putting out 13.2 (which is enough to maintain a battery), I'd suggest a bad diode letting the battery discharge.
If it was dead after 3 hours with the alternator putting out 13.2 (which is enough to maintain a battery), I'd suggest a bad diode letting the battery discharge.
Originally Posted By: Back40
This is my daughter's car. She called yesterday and told me the battery was dead after being parked about 3 hrs from returning from the doctor. She had it jumped and said the alternator light in the dash was not illuminated and drove to Autozone where they provided the 13.2 voltage reading and suggested the alternator. I will be heading over tonight with my battery charger and multi-tester. If I confirm the voltage output at 2000 rpm is low 13s then I guess it's time for a rebuilt altenator.
(removed insult)
It is possible your alternator is only providing 2/3 or 1/3 or it's ability, but I do not think so. I think your alternator is fine and it is the battery which is weak/ old/ sulfated and definitely undercharged.
If a battery needs a jumpstart, it was obviously near dead. The vehicles charging system will need Hours and hours of driving before it can fully charge a battery. There is no way around this. A battery can only accept so many amps so thinking an 85 amp alternator is recharging the battery at even half that rate for any duration is unlikely in the extreme.
The battery might have been 30% charged when Autozone took a 13.2 reading. If they had revved the engine they would likely see the voltage climb. 13.2 volts at idle speed with a severely depleted battery is to be expected. At Idle speed the alternator might be able to produce 30 to 40 amps. This is not enough to bring the voltage above 13.2. After 10 minutes, sure the voltage will start to rise more. As the battery increases in charge the voltage will rise. When it gets to the factory set point, the voltage regulator will start asking less of the alternator to keep the alternator from bringing the battery voltage above the setpoint, which will change with temperature.
Also the opposite is true. When the battery is at or very nearly fully charged, the voltage regulator will drop the voltage to 13.2 to 13.6 so as to not overcharge the battery and cause excessive water consumption.
Whenever a battery needs to be jumpstarted, it is best to plug it into a regular 10 amp battery charger overnight. If after doing this, the vehicle needs another jumpstart again, the battery is done.
If the vehicle is only driven less than an hour after a jumpstart the battery is still likely below 50%. It will have enough juice to start the vehicle, but anytime a battery is sitting below 80% charged it is sulfating, losing life and capacity. SO a bunch of short trips never will get th battery above 80%, the battery dies early and the owner blames the vehicle or the battery.
This is my daughter's car. She called yesterday and told me the battery was dead after being parked about 3 hrs from returning from the doctor. She had it jumped and said the alternator light in the dash was not illuminated and drove to Autozone where they provided the 13.2 voltage reading and suggested the alternator. I will be heading over tonight with my battery charger and multi-tester. If I confirm the voltage output at 2000 rpm is low 13s then I guess it's time for a rebuilt altenator.
(removed insult)
It is possible your alternator is only providing 2/3 or 1/3 or it's ability, but I do not think so. I think your alternator is fine and it is the battery which is weak/ old/ sulfated and definitely undercharged.
If a battery needs a jumpstart, it was obviously near dead. The vehicles charging system will need Hours and hours of driving before it can fully charge a battery. There is no way around this. A battery can only accept so many amps so thinking an 85 amp alternator is recharging the battery at even half that rate for any duration is unlikely in the extreme.
The battery might have been 30% charged when Autozone took a 13.2 reading. If they had revved the engine they would likely see the voltage climb. 13.2 volts at idle speed with a severely depleted battery is to be expected. At Idle speed the alternator might be able to produce 30 to 40 amps. This is not enough to bring the voltage above 13.2. After 10 minutes, sure the voltage will start to rise more. As the battery increases in charge the voltage will rise. When it gets to the factory set point, the voltage regulator will start asking less of the alternator to keep the alternator from bringing the battery voltage above the setpoint, which will change with temperature.
Also the opposite is true. When the battery is at or very nearly fully charged, the voltage regulator will drop the voltage to 13.2 to 13.6 so as to not overcharge the battery and cause excessive water consumption.
Whenever a battery needs to be jumpstarted, it is best to plug it into a regular 10 amp battery charger overnight. If after doing this, the vehicle needs another jumpstart again, the battery is done.
If the vehicle is only driven less than an hour after a jumpstart the battery is still likely below 50%. It will have enough juice to start the vehicle, but anytime a battery is sitting below 80% charged it is sulfating, losing life and capacity. SO a bunch of short trips never will get th battery above 80%, the battery dies early and the owner blames the vehicle or the battery.
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Sorry about the insult. I would like the posters in this thread to know it was directed at some AZ employees, and not anyone who responded in this thread.
I'll refrain in the future.
I'll refrain in the future.
Update - I tested the voltage (Multi meter set to 12V batt) at the battery with the engine idling and got any where from 13.8-14.3. So, not sure where to go from hear. I am a novice at diagnosing electrical probs so I appreciate everyone's feedback. I hooked up the battery charger and set to 2mp charge overnight.
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13.8 to 14.2 volts is fine.
2 amps each hour overnight did not fully charge the battery. If the charger is automatic and not manual, set it to 10 amps and let it go. If it is a manual charger, give it 2 to 3 hours at 10 amps then switch to 2 amps.
If the battery needs a jumpstart anytime soon, either the battery is dying, you daughter is leaving the stereo or lights on too long after engine shut down, or some other device is drawing too much electricity with the engine off.
13.8 volts shows the alternator is charging the battery. Every time a battery needs a jumpstart, it has lost a portion of it's capacity. If it is not put on a regular charger quickly the capacity lost will be greater. With winter coming/here you might consider a new battery, or buying a jumper pack and instructing you daughter in it's use. Also promptly recharge the jumper pack after each use, or monthly if not used.
2 amps each hour overnight did not fully charge the battery. If the charger is automatic and not manual, set it to 10 amps and let it go. If it is a manual charger, give it 2 to 3 hours at 10 amps then switch to 2 amps.
If the battery needs a jumpstart anytime soon, either the battery is dying, you daughter is leaving the stereo or lights on too long after engine shut down, or some other device is drawing too much electricity with the engine off.
13.8 volts shows the alternator is charging the battery. Every time a battery needs a jumpstart, it has lost a portion of it's capacity. If it is not put on a regular charger quickly the capacity lost will be greater. With winter coming/here you might consider a new battery, or buying a jumper pack and instructing you daughter in it's use. Also promptly recharge the jumper pack after each use, or monthly if not used.
Thanks wrc!
Sounds like the battery is dead, and if it's the original it is at least 5 years old, which is about max life in my experience. But, first make sure you've got clean and tight connections at the battery terminals. Lots of times I find that a poorly charging battery is the result of loose or corroded terminals.
Toyota charging systems are fickle - I know when the AC Delco reman alt in my Lexus gave up the ship it lit the charge warning lamp ONLY when the brushes are worn out and the alternator output was below battery voltage. I put in new brushes and new bearings and the alternator tested fine on Kragen's bench but it didn't charge the battery fully when I hooked up an Sun VAT-40 tester - the hot output was below 13.5V and the alt threw out 90amps. Even though the alternator's moving part and stator checked out, the alt was a bad reman.
I replaced it with a Denso reman, replaced the frayed wiring plug and all is good. I'm at 14.4v cold, and between 13.7-13.8v hot but I need to have a VAT-40 hooked up to it for load testing.
Moral of the story - CHECK your wiring, check your battery and replace/recharge it if need be. And use a Denso reman if you can afford it.
I replaced it with a Denso reman, replaced the frayed wiring plug and all is good. I'm at 14.4v cold, and between 13.7-13.8v hot but I need to have a VAT-40 hooked up to it for load testing.
Moral of the story - CHECK your wiring, check your battery and replace/recharge it if need be. And use a Denso reman if you can afford it.
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