Temporary inop alternator

Hey all,

Had a problem last night, started my truck and the battery wasn’t charging/warning light was on. Shut it off and restarted, light come back on within seconds. Checked voltage via my head unit, read 11.9v with the lights and blower on. Started just fine, didn’t crank weakly or anything.

After maybe 15seconds, the alt finally kicked in with a brief slight belt chirp, warning light went out, and voltage jumped to 13.9v. Eventually settled to 13.2-13.4 on my ~30min drive home. Not sure if the HU gets the voltage from the OBD port, the ECU, or just measures its power feed. I imagine the ecu, where it gets all of its other scangauge-type readouts.

We had some heavy rain while it was parked, but it was not run/driven in it. The belt was not squealing while the light was on. Battery is about 2 years old and I’ve done no electrical mods in the past few years. Should I be planning to replace the alternator soon?

 

How many miles ,original alternator?

 

Just hit 207k on the drive home, and yes, original alternator.

I’ve just never seen one glitch like this. Usually they get weak till they stop charging altogether. Wanna make sure I’m not missing something before I replace it.

 

First check for any corrosion or loose connections at the alternator (large wire and connector) and also at the battery. The battery connections, not visual but actually clean them.

 

Check the belt tensioner too. This could be a loose accessory belt.

Bad grounds cause a lot of odd electrical issues too. If you can get the problem to repeat itself then using jumper cables from the battery negative to the block can expose a bad ground situation.

 

The alternator is going out, time to replace...
its what they do, light comes on, light goes out, intermittently / randomly..
Very, very common....
Its that simple..

 

Good point, I’ll go through the connections and ground and clean them up.

I’ll check the tensioner but I doubt it’s that. There was no squealing or anything, I was listening as that was my first thought in the moment.

In my experience, the light coming on intermittently can be a symptom when the alt is weak and producing borderline voltage. But I’ve never seen it go from working fine(I monitor my voltage regularly), to totally dead, and then come back to healthy nominal voltage without something else contributing to the problem. I’m wondering if moisture (or corrosion)got somewhere in the sensing or field circuit and tripped it out briefly. Just trying to get a full picture before my broke ass loads up the parts cannon lol.

 

Here's everything on the charging system if you want to check it all but do note if it's working everything will likely test good, ideally need to test when it's not working.
It's not uncommon for the wires to get nicked and corroded near the connector on the alternator.
https://www.tacomaworld.com/threads/2nd-gen-information-diagnostics.784008/#post-28042155

 

Thank you for that, much appreciated. Hoping it was just an isolated fluke I can fix by wire brushing some grounds. That battery light was the last thing I wanted to see after a long wet day.

 

I get that & what's your saying makes sense...
Same time, not one electrical component will fail the same every time, every scenario can be different.
Nothing wrong with cleaning things up & monitoring the situation.
Could be early stages of internal defect & if so, still may be 6+ months out of it, or could totally fail tomorrow.
Funds are a concern, do what you can, monitor,
Carry a jumper pack with you if you have one, dont go buy one for this....

 

Sounds like the alternator might be cutting out intermittently. I just went through this on my wife’s Kia. I confirmed it with a data log, you could see the voltage graph dip and then come back up to spec while driving. Most of the time, once they start doing that, they eventually quit altogether, but they can definitely act up intermittently before failing completely.

 

borrowed time...

 

One of my old Cherokees did the same thing, the volt meter first randomly started taking few seconds to come up to normal on start up. The occurrences got more frequent and longer.

I came out of work one night and drove more than a mile before it woke up - I called that my final warning, a new alternator fixed the problem fortunately.

 

Hmm, looks like I’ll be planning to need a new alternator soon then. I’ll take the time today to test what I can and clean up the connections and grounds, and monitor it for any further hiccups. If it gives me any more trouble, I’ll bite the bullet and replace it.

Thanks for the input, all. Learn new things everyday. I’ve seen alternators fail by way of getting weaker over time until they couldn’t charge the battery, and those that give up the ghost all at once. But I’ve never seen one that died on startup and came back to life like nothing happened. Which made me think an outside factor like moisture or corrosion played a role.

 

Minor update: duplicated symptoms (duh) by unplugging the alternator. Felt a little crusty coming out. Cleaned it out a bit and firmly reseated it. Voltages seem to settle about .2v higher now, 13.4-13.5v as opposed to 13.2-13.3v. Both warmed up with headlights and blower on.

 

Still running a little low on the output side. Normal charging voltage should be in the 13.8–14.5v range. The good news is alternator replacements on Tacomas are an easy driveway job.

 

Not for a 2nd gen, they run in the 13.2-13.8 range typically. The hotter it is the lower the voltage. Only time I've ever seen mine over 14v was on a very cold day.

 

Mine puts out 14.2 cold and around 13.8 driving around...but you are correct, I stand corrected, thanks for the knowledge.

 

Replace the alternator ASAP or your next ride home could be in a bigger Toyota truck (Hino flatbed).

 

I've saved a date when her FJ died on the side of the road. I brought her a charged battery and got her to my house. Swapped the alternator in the garage while she made me dinner as a thank you. It worked well!

But yeah, a dead alternator sucks. but you can drive as long as you have enough battery to run the ignition...

This does not work on a lot of modern cars since their power steering is electric. My 2019 Daily Driver has electric steering.