Poll

What's wrong?

Only registered users are allowed to vote for this poll.
21 votes were received.

Alternator	7		33%
Short	2		10%
Corrosion, loose connection	2		10%
Ghosts	5		24%
Battery	5		23%

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Last week, my car's battery was dead. Doors wouldn't even unlock. I used a jump start battery thingy (JSBT) and it was fine, worked all day, would start right back up.

It's an '06 Highlander with 150k miles. It's the original alternator. This car is tough on batteries. My mechanic couldn't find anything to explain that a couple years ago, said the alternator was fine, maybe I'm always leaving the lights on. I'm not. I always have the JSBT with me and I'm an old hand at replacing the battery in this thing.

I don't drive a lot so it sat in the driveway. This morning it's dead again, won't even unlock the doors. I used the JSBT, thinking I'd go buy new battery. It started right up, ran for four seconds, died suddenly. With the JSBT hooked up, it won't start, no lights on the console, nothing.

If I wait twenty minutes and try it again, the exact same thing happens. Runs for four seconds, dies suddenly, acts like the battery is disconnected.

So what's up? I can replace the alternator myself but probably nothing more difficult than that.

I would guess either the battery has a short or the alternator is bad. You could take them both out and take them to an reputable auto part store for testing.

If it was me, I'd replace the battery and then if I still have a problem I would replace the alternator. If there is STILL a problem then you have a wiring problem.

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It's may be a combination of both a short and the battery being completely discharged because you haven't charged it up sufficiently. I would strongly advise against replacing parts willy nilly without conducting some straightforward diagnostics. You could easily replace both the battery and the alternator and still have the problem.

Unless you went on a really long trip, the battery is still at a low charge level and you need to put it on a charger for a couple of days. No, attaching a jump starter is not a substitute for charging. It may also be that your battery is now fried from being completely discharged so many times. sometimes when they get that low it is difficult to get them to take a charge initially and they can act as though they are shorted out. I would pull it, get it charged up as much as possible, then take it to a battery shop for load testing (usually free).

It's extremely easy to assess alternator health. Simply check the voltage across the battery terminals with a voltmeter both at rest (should be 12-13 volts) and while it's running (should be about 14 volts). Then turn on a bunch of loads (AC, lights, etc) and see if it remains stable. If it stays around 14 volts then it's unlikely that the alternator is bad.

To test for shorts, make sure that you have your radio code since you need to disconnect the battery. Turn everything in the car off, disconnect the negative battery lead, and clip the positive voltmeter lead securely to the disconnected lead and the negative voltmeter lead to the negative battery terminal. Switch the voltmeter to amps with the range set to about 200 mA. There should be a parasitic draw that you can measure of between 10 and 50 mA. Any more than this and you have a problem in your car wiring or electrical components somewhere. Start pulling fuses to zero in on where the problem is. I had this exact problem last year on our Acura. It turned out to be a faulty cell phone linking module which got stuck in the "ON" position 24/7 and was sucking the battery dry.

By the way, if your mechanic throws up his hands at the problem of your vehicle going through too many batteries then you need a new mechanic. This stuff is all Basic Auto Mechanics 101.

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Edited 3 time(s). Last edit at 10/19/2021 12:31PM by davester.

What davester said. Slap a real charger on it right away. Also, if you jumped it from another vehicle it would stay running.

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It should be easy for a competent mechanic to check:

status of alternator
status of battery
potential 'leaks' when ignition is off.

There may be no 'short' in the typical sense as most involving 12+ to ground will blow a fuse.

A DMM would reveal any current drain from the battery with the ignition off, and whether it's excessive or not.

Most radios use some juice to keep the stations in memory, but that doesn't take much.

It might be that a back connection (sometime a ground/earth connection) might allow for weird path for current to flow with the key off, that doesn't blow a fuse but allows for a significant drain.

Monitoring the drain on a DMM while pulling selectively pulling fuses can help isolate the drain.


With a proper battery charger and a DMM, you should be able to check the charging circuit, assuming the car starts and runs.

If it does, the alternator should measure at about 14.5V, and is probably OK.

Then I'd pull the battery and have it load tested.

Regardless of any other electrical problems, if the battery is bad, it will have to be replaced.

If the battery and alternator check out, then the fun begins tracking down a drain with the key off.

That seems the most likely suspect given your mechanic apparently can help with a simple alternator/battery fix, and that your vehicle as 'always been hard on batteries'.

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My mechanic couldn't find anything to explain that a couple years ago...
Just a suggestion, find a shop that can run a diagnostic on an '06 Toyota.
Even back then, Toyota had a pretty good ECU/Data system.
btw, a diagnostic is not the same as pulling OBD codes.

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First I would take it to Walmart or a parts place and let them run what ever free battery and alternator tests and Check Engine light (even if it’s not on) test they will.

Quote
Dennis S
First I would take it to Walmart or a parts place and let them run what ever free battery and alternator tests and Check Engine light (even if it’s not on) test they will.

Umm, Walmart better be close if it only runs for four seconds.

Quote
PeterW

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Dennis S
First I would take it to Walmart or a parts place and let them run what ever free battery and alternator tests and Check Engine light (even if it’s not on) test they will.

Umm, Walmart better be close if it only runs for four seconds.

Hopefully the lights will be with him.

What davester said: battery. It's very possible it is the alternator, but you'll need a good battery at least. You can test the alternator output, some easy (relatively) tutorials out there.

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Both the battery and alternator can be tested fairly easily. I'd do that before I started randomly guessing and replacing stuff.

I'd just randomly replace stuff. Start with the floor mats.