Battery light stays illuminated for a while after each start

[Mr Ree]

Hi TS'ers.

Lately, and typically on the first start of the day, my 1997 SXV10 Camry wagons (5S-FE) battery light stays illuminated for anywhere between 2-45 seconds, then goes off. This has been happening for the past two weeks, and with no other symptoms to lead me to believe the alternator isnt working, or the battery isnt charging. The battery is years old and still the headlights and other electrics work perfectly at night, with no fading as you would expect with a failed alternator. (Multimeter isnt at my home so need to dig it out and confirm my theory, but given its still working now, I can reasonably assume that its still charging fine)

I have googled this and researched the problem, which seems to be fairly common from what I could find, often being a simple $5 diode that fails in the alternator, but I was just wondering if anybody here had soldered this diode in your own toyota alternator, and if so, was it as simple as ordering it from toyota and installing it, or does the alternator need to be disassembled to do it?

Thanks for any help of advice anyone might have

[Jdawg]

Try swapping your battery for a good one first, it may be tired. Winter time taxes a battery a bit harder.
Alternator needs to be stripped, in the old days it was worth the effort, would have thought it would be easier to replace alternator if it was shot.

[siren676]

Might not be the same issue as yours but its an easy check.
My starlets charge light was doing that when the terminal on the charge cable had come loose. The charge light would sit on for a few seconds after startup or would go out if i gave it a rev.

[Mr Ree]

Thanks for both of your replies

The battery is still strong as hell. Cranks like a new one, but yes, I will test its voltage very soon when I check the charge output of the alternator. I hope I dont need a new alternator as I wouldnt like to think what an OEM item will cost lol

Yes, I have gone over all of the teminals and connections too, but am going to remove all earth straps and battery/alternator connections and use electrical cleaner inside plugs etc. Alot of times, this fault seems to be nothing more than a poor connection or bad earth, so Im crossing my fingers that this is the case for me too hehe

[gepsk8]

still could be anything,
Main thing is check belt tension and condition
loose connection on alt and battery
any battery shop can test ur battery for free, could be issue
maybe alt take couple of photos of front and rear, post them or pm them if its bosch model maybe reg(common), nippon common for faulty regulators and rectifier maybe not worth fixing

[Mr Ree]

I had completely forgotten about starting this thread last winter, as the problem stopped happening once the weather warmed up a little, so I didnt give it another thought....until now.

Now, with winter here, the problem has started happening again.

It only does it on cold mornings and/or the first start of the day if it hasnt sat in the sun for hours warming up. So the problem seems to be entirely related to ambient temperature.

Im still running the same battery, and have never had an issue with it being flattened. It starts quickly, every time, without fail.

Also, the battery light can be made to disappear by revving the engine up to around 3000-3500rpm which matches with what "Siren 676" stated.

[GDII]

What is your belt tension like? After I did an engine swap and put the belt back on it wasn't as tight as I normally had it so after washing the car the belt would slip until it heated up and got some grip. The MR2 has a lovely water channel on the engine lid directing water directly onto the pulley so that's why my car did it. After I tightened it up I've not had a problem like that since.

[Mr Ree]

Thanks for your reply.

The belt is tight enough, but I guess it could be slipping initially on freezing cold mornings.

Im thinking its more likely to be a failing diode in the alternator that tells the battery light on the dash to turn on/off though.

[GDII]

Diodes usually work or they don't. The voltage regulator could be failing, this is something that is hard to test at home.
Diode checks can be done easily with a multimeter at home and I assume doing it on a Camry is far easier than an MR2.

Also the slip ring or brushes could be wearing out. Toyota's alternators have very thin rings that wear out easier.

[Mr Ree]

Would you mind please describing the procedure for testing the diode? I have a multi-meter in the cupboard so thats not a problem.

What brand of alternator would you recommend I look to buy if the OEM one decides to finally shit the bed?

Thank you

[GDII]

This is a good video on a simple test for diodes.
https://www.youtube.com/watch?v=xgikeXt91vM

Depending one what is wrong with the alternator then you would get it rebuilt or if you need a new one then a Denso one would be best as that is actually what the OEM ones are.

If the diodes are dead then you can get replacements ones. If the voltage regulator is dead then you can get a new one too. If the bushes are worn out you can also get new ones but I think they are part of the voltage regulator. If the slip rings are worn then that is a bit more expensive. Budget for anywhere between $100 to $600+ for parts or a new one.

[gepsk8]

OEM don't make alternators.
Will be Nippen Denso or Bosch
Have u even checks the brushes?
Slip ring ok?
Bearing ok?
Good luck swapping diodes, if diodes are even the problem,
best to buy new rectifier, Gud luck swapping old ones out

Best take picture of it.

[matt dunn]

You cannot correctly test alternator diodes without dismantling the alternator.
If you are testing them in place, you might as well not even bother turning the multimeter on.

The recifier will have either 6, 8 or 9 diodes in it,
and it only takes 1 faulty one to cause problems.
You cannot replace indvidual diodes, they are all usually made as one part.

My guess would be bad connection between the alt and battery if a denso unit
or faulty regulator if a bosch one,

[sergei]

You cannot correctly test alternator diodes without dismantling the alternator.

Unless you have a oscilloscope. Old analogue will do.

Blown bridge (1 diode shorted):


Good bridge:

[matt dunn]

Still does not always show up even on them,
I know as we have tried many times on cars where taking the alternator off is not easy,
and we have a couple of good oscilloscopes, and have still pulled them off to find a blown diode at times.

Can depend a lot on if the stator is star or delta wound and if the number of diodes.