I had a question about the battery light on the dashboard. Below are the specifics:

• 2005 Scion tC
• Battery was just replaced in July
• With a multimeter, I measured battery voltage: ~12 V (engine off) / slightly less than 12 V (engine on)
• I haven't driven my car a lot during Covid. I took my car out for the first time in 2 months on Friday. the battery light came on.
• I have applied a trickle charger to the battery for 9 hours total (charger started at 9 amps and I disconnected at 3 amps). I may trickle charge some more tomorrow.

When I just tried to start my car, the battery light is still on.

Is it required to disconnect/reconnect the battery to reset the battery light or is a problem still being detected by my car?

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Battery should be at about 13.8V with the car running, definitely not less than when the car is off, if it's charging properly...have you had your alternator tested as it sounds like that might be the issue.

 

Malfunction lights indicate a problem with car. Fix the actual cause/problem that's triggering light to come on rather than just trying to dismiss it. It's like ignoring the low-petrol light, won't solve low tank issue and can cause extra headaches if you ignore for too long.

Battery light is technically called "charge lamp" and has nothing to do with battery. They should really use different symbol. It means there's problem with your alternator and for whatever reason, it's not putting out enough power. Over time, battery voltage will drop lower and lower and you won't be able to start car. Not battery's fault if it's not being recharged.

Get alternator inspected, most often it's just regulator that needs replacing. If you're handy with soldering-iron, you can usually replace diode that has failed. Once alternator is fixed, light will go out and battey will be recharged to proper 13.8v. Do it soon, because using battery in depleted state will destroy it and you'll have to buy another new battery.

 

Thanks for your comments. I am almost certain that this issue is real and has to do with the alternator. I have finished trickle charging my battery. When the engine is off, the voltage at the battery is about 13.5V. When i start the car engine, the voltage at the battery terminals drops to 12.5 V. Therefore, the alternator is not producing any current, I think.

A couple of things i noticed while the engine is running

• There is no abrasive or harsh sounds from the alternator, so I don't think this is a bearing failure issue.
• The pulley is spinning ok, so I don't think this is a belt slippage issue.

Is there anything else (maybe a fuse?) I should check before I bring my car into the shop to replace the alternator?

 

Go to some local auto parts store and they can run a test on your alternator...

 

Battery voltage will always drop after starting. Then it takes 5-15 for alternator to recharge battery. Measure battery again after 10-minutes, is it higher or lower than just after starting?

Nothing more you can do really. Can test it with multimeter to verify that regulator diodes has failed. Auto-parts store has automated machine that does this easily. Takes about 30-min to remove & re-install alternator. I've done this in parking-lot at school in middle of night.

 

OK. i will start and run the car for 10 min and re-check the voltage (after 10 min with car running, right?).

btw, if i replace the alternator, should i also change out the serpentine belt? it's 16 yrs old as well.

 

Not a bad idea while you're there.

 

thank you, everyone, for your time and advice. i hope to get this resolved soon.

 

One last question:
Where is the best place for me to get a replacement OEM denso alternator? I called the parts department of my local car dealership, and they quoted $440 just for the part.

 

I'd look at the usual suspects...RockAuto, Amazon (but make sure it's genuine as there have been known to be some counterfeit on there), I'd avoid eBay altogether or any of the online Toyota parts dealers, I've found Sparks TRD usually has the lowest prices with shipping figured in.

 

Thanks!

it seems like remanufactured alternators are the predominant option. does anyone have an opinion on remanufactured vs new?

 

Re-manufactured can be hit-or-miss depending upon who has done the rebuilding. I'd look at some of the re-mans and check customer feedback and warranty/replacement terms.

You could also look locally to see if there is someone who could rebuild it as that way you've got local access should something go wrong.

 

I haven't had any issues with rebuilds from FLAPS. Make sure they used Denso as core and offer lifetime warranty. Some models like Corollas, has U.S. built vesions using AC Delco alternator. Don't want one of those!

 

thanks, all. i ended up deciding to bring the car into the shop to replace the alternator (remanufactured denso) and belt. for a minute there, i considered doing this myself, but i wussed out.

thank you all for your time and wisdom.