Camry: bad alternator?

One day last week my wife noticed that her 2004 Camry seemed “weak” when she went to start it. Yesterday she drove to the post office, came out to start the car and the only sound it made was the cd player chattering. Yesterday after work I went to retrieve that car, it started fine. I then went to a local parts shop where they hooked an electronic tester to the battery and had me start the car. I was then told that the starter and battery were fine, but that the alternator had bad diodes. Could it be the alternator? The same thing happened me about 3 years ago, it was the battery. I would have thought battery or starter?

Get a second opinion. A battery is only as good as the alternator keeping it charged. It’s probably the alternator.

Yup. It could be the alternator. Is there a specific reason that you doubt their diagonsis? This is, after all, not an uncommon problem.

While it could be the alternator, a weak/bad alternator would cause a battery to be low on charge. The parts shop should have told you that. The battery could be perfectly good like the parts shop said but it would need a charge and they should have detected that. Your symptoms are consistent with a low charged battery. Anyway, if you have access to a battery charger, now would be a good time to use it.

The only reason I doubt their diagnosis is the no-start followed several hours later by a no-problem start (several in fact). I’ll be replacing the alternator this evening. I’m just concerned it could be the starter and she’ll end up stranded.

Your logic is excellent.
You may ultimately have an intermittent starter as well, however bad diodes in the alternator are definitively verifiable on test equipment, and I’d be inclined to believe their diagnosis. It is possible that you had both problems and they were unable to verify the bad starter but did find the bad alternator.

I’d get the alternator changed and if you still have a problem keep the starter in mind as a possibility.

Get an alternator with a lifetime warranty.

It sounds like you have both a bad starter and a bad alternator (at least the test says so about the alternator).

When my starter was failing, it started out that I would occasionally have no response when turning the key. I mistakenly replaced the battery and it got a little better at first, but eventually I would have to turn the key more and more times with no results before it would “catch” and start fine.

It was explained to me that the starter had developed “bad spots”, and when I turned the key, it would turn the starter a little each time until it finally hit a “good spot” and started the car. I’m sure others here will know the proper terminology.

The difference was amazing when I replaced it. It was even better that I found a starter which had recently been replaced at a salvage yard for $12.50 and my labor was free.

I replaced the alternator last night, started the car and let it run for a while then drove it around for a while. This morning the temp had dropped to 50 F and the car truned over, but weakly…

As temp drops - it takes more energy to turn the engine. As temp drops, the available amount of energy from the battery - also drops.

Go out and measure this evening or tomorrow morning - the no-load voltage of the battery. Before you try to start it. Just pop the hood, take your vom and measure the voltage. Should be around 13…2 - 13.5. Now, briefly turn the headlights on; how low does the battery voltage drop. Shouldn’t be by much. ( say 12.5)

Now, start the vehicle. Measure the voltage at battery with engine running, lights off. Should now be around 14 If not 14v; you have a problem with the newly replaced alternator, or something not letting it work correctly.

If no load battery voltage (engine not running) is not around 13.2 - the battery either needs fluid (electrolyte); charging (alternator working good?) or should be replaced. How old is the battery? Seven years is getting up to max (for reliability); and care/maintenance; and correct charging and vibration can all have negative effects. Since this is a 2004 Camry - if it is the original battery - it does need to be replaced.

@DS777 with all due respect, where is your 13.2v figure coming from?

A good battery should measure 12.6v across the terminals.
After any surface charge has dissipated.

A battery might read 13.2v across the terminals right after a charge.

If somebody applied your 13.2V figure as a test of a battery, they might condemn a good battery!

Yes, I see where your coming from. Not trying to cause someone to throw away a good battery. However a battery which is just sitting and not doing much except for maintaining the low current clock etc. will have a 13 or so voltage. At least some of them will. For example, the battery in my own car… But yes, technically, at 2 volts per cell a good battery reads 12v. But generally a battery not doing much - reading 12v needs to be charged or more fluid or replaced. That’s where I’m coming from… However - from the op description and posts - I suspect the battery has a problem or something is not allowing it to be charged correctly. Even though the parts store meter stated it was ‘ok’.

You are correct. I was in error on battery voltage. My own vehicle’s battery voltage is 12.5. Got my numbers off; I do apologize. Thank you for pointing it out.


No problem.

50 F is not very low in respect to starting the car. If it was 20 F, that would be different.

I would definitely test the battery before you go to start it in the morning. If the voltage is close to what @db4690 mentioned above, then I would replace the starter.

What’s a little suspicious to me is that I don’t think it is possible to confirm the battery is good unless it is fully charged at the time of the test. And if they say the battery is good, then it must have been fully charged. But how could it be fully charged if the alternator is bad?

On the other hand, I guess it is possible that the car’s recent operating conditions, the alternator was able to put out enough juice to charge the battery; esp if the car wasn’t driven with the headlights on at night, or in other situations with a large electrical draw, like running the radiator fan or heater blower fan. It’s possible just driving about town during the day an alternator 3 diodes short of a full working set could still charge the battery. And the diagnostic equipment most shops use should be able to detect faulty diodes without much ambiguity. So the alternator is probably faulty in any event.

Has this car been recently jump-started? Or used to jump start another car? Those events are probably the most common reasons for alternator diodes to be damaged.

If replacing the alternator doesn’t solve the starting problem, ask your mechanic to check the voltages at both terminals of the starter during attempted cranking. If either is below 10 volts, that is a problem and needs to be understood. Could be something as simple as corroded connections somewhere. If both are above 10.5 volts during attempted cranking, and the starter doesn’t crank the engine, it’s probably a faulty starter or starter selenoid contacts.

I’m pretty sure this was a bad battery from the get-go. I installed the new alternator, drove it for a while to charge the battery and then went back and had the system retested. I was told the battery was too weak to tell if the new alternator was good or bad. When I questioned the previous night’s test I was offered a free battery replacement. No problem in over a week now,

DB4690 is dead-on correct about the 12.6 volt figure. Six cells at 2.1 volts each on a good battery gives you the sum total of what it should be and from personal experience I’ve never seen or heard of a 13 volt battery reading.