2013 Toyota Sienna Bad Alternator

I'm almost positive I have a bad alternator on my 2013 Toyota Sienna 3.5, but just wanted to check and see if there's anything I missed.

Symptoms: battery light on dash is always on with engine running.
Low voltage across battery terminals with engine running- about 12.0V with no accessories on, drops to 11.4V with some big loads turned on (headlights, rear defogger, front and rear blower motors on full blast), voltage goes back up to 12.2V with engine off.

Troubleshooting done so far: hooked up my electronic battery tester- battery tested good, starting circuit good, alternator bad. The alternator test said "diodes good, regulator good, output bad"
Disconnected battery terminals, cleaned them up, reconnected and made sure they're tight.
Did a voltage drop test- first I tested the negative cable by removing the fuel pump relay and cranking the engine. I measured the voltage between the negative post and the engine block while cranking. The voltage was about .07V. Then I tested the positive cable- I reinstalled the relay, started the engine, and turned on the big loads listed above. Voltage between the battery positive post and the alternator post was around .05V.
I disconnected the electrical connector on the alternator just to check for corrosion and condition. It looked perfect.

Is there anything else I should check before condemning the alternator? I wish I had a diagram for the charging circuit, but I don't. I used to use BBB Industries for diagrams, but their website has become so glitchy it's unusable.

There's only a couple more checks I'd suggest before replacing the alternator. At the four pin connector on the alternator, you should have green, red, blue and white wires. Green is a constant power from the ALT-S fuse. Red is ignition power from GAUGE #1 fuse. Blue is a load feedback to the ECM, and white is the light control circuit (which we know works because the battery light is on).

The blue feedback circuit is exactly that, and won't influence the charging rate. White is good, which leave green and red. With the engine running and the alternator not charging, both should be pretty close to battery voltage. How close, exactly? Depends on who you ask. :silly: Hopefully within 500mV.

If those two circuits are good, I'd say you're good to put an alternator in it.

As above , when diode packs fail voltage drop testing tends not to show anything anyway because there is minimal current flowing out of the alternator.
Some Japanese alternators it is really easy to change the diode pack together with the brush assembly but getting the correct parts can be a hassle so a a replacement is the best bet.

I checked the voltage on those wires and they were good. I just replaced the alternator and it's fixed. No more battery light on the dash and I'm getting 14V across the battery terminals now. Thanks for the help!

Yes a funny thing with alternator diode pack failures testing withjust a multimeter they can actually look as if they are charging fine,