[10silver]

Over the past three weeks or so I have been having problems with the charging system. I am on the 3rd alternator right now. The first two I purchased from advanced auto parts and both were putting out low charging voltage about 12.5-12.6 approx. so I got a refund. Then I decided to try one from oreilly which I have in the car currently which is also putting out low voltage. I went to the dealership yesterday and they said this one is putting out 12.45 volts. The battery is brand new and tested good but needed a charge put on it (12.48 volts).

I'm trying to understand why all three of these alternators could be at a low charging voltage. Do I need to go with a toyota brand alternator or would I just be wasting my money? I'm lost.

 

[somick]

I believe the problem is the aftermarket junk. I am pretty sure that OEM will be working fine but the price difference is humongous.

Since most of auto parts stores give you a lifetime warranty keep trying. At least that what what I would do.

Good luck,
Sam

 

[10silver]

Thanks for your reply. Now second question what about buying a used alternator for a 2010 corolla from a 2010 with low miles (around 30k miles) for around $100 or so?

 

[cj1]

High resistance wiring/connectors from alt+ to bat+ and alt ground to bat - can cause low v at battery. Also a slipping alternator clutch will cause low v at alternator.

Is the low voltage measured on the battery terminals or bat cable connectors or at the alternator?

 

[10silver]

I measured it with the positive lead from the multimeter on the B+ post on the alternator and the negative lead from the multimeter on the negative post on the battery.

 

[cj1]

So low voltage directly from alternator, charge warning light is lite?
Does revving engine increase voltage, cause warning light to go out?

 

[10silver]

Battery light is not on (Battery light does go on when car is started then goes out). Lights are not dim and don't get brighter when I rev the engine. I did a voltage drop test also and everything was normal.

 

[Chuy]

Are you checking the voltage at the alternator and inside the cab at the power port to see that the voltage output is the same? If voltage is not near identical, you likely have a bad connection somewhere (a half volt difference is acceptable).

Next alt you get from Oreilly's, have them bench test it first.

I got an Oreilly's alt for wife's Lexus and it puts out 14.1 volts. It did go bad after 22K miles - the voltage regulator started putting out 11.5 volts. Oreilly's provided a new reman under their lifetime warranty - going on 10K miles.

 

[cj1]

Last straw, back probe the four pin connector to verify voltages.

Pins 1,2 should read bat v. Pin 4 alternator output v and pin 3 a PWM voltage from ECM. ( dealer can verify this if not all ready done)

The alternator v range is controlled, within a volt or so, by the PWM voltage from the ECM.
Not certain if the 12.5v you read can be a result of low PWM voltage. The range may be more like 13-14v.

As Chuy mentioned, verifying the correct alternator voltage on the bench before the install, is the first step.