Battery light

BGRANILLO

MEMBER
2000 MAZDA PROTEGE

Four cylinder two wheel drive automatic 90,000 miles.

My battery light was on and I was told I had a bad alternator. I switched it out and everything seemed okay and the light went off. Two days later the light comes back on. I take it to the shop where I purchased the alternator and they test it while the vehicle is on and they say they cannot get a reading off the alternator. They ask me take it off and return it. After removing the alternator they check it in their machine and it passes with flying colors. My battery is also fine as far they can tell. I do not know why the alternator would not register on their gauge. Could it be a a fuse causing the light to go on? Could the battery not have enough charge? Is one of the lines from alternator to the battery bad? If so how can I test that. I thank you for your help and let me know if you need any more information.

3 Replies

KHLOW2008

MECHANIC
41,814 POSTS

Hi bgranillo,

Thank you for the donation.

First you should test the charging at the alternator. Connect a voltmeter to alternator main post and engine ground. With engine off, you should have battery voltage. If battery voltage is not available, the connection between battery and alternator is bad. Check for a blown fuse in under hood fuse box.

With engine running, it should be between 13.5 to 14.5 volts. If reading is correct, connect voltmeter between battery terminals. Charging should be similar to above.

Here is a schematic of the charging system and you can refer to it for which fuse to check:

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Wednesday, June 17th, 2009 AT 1:59 PM

EL DONGO

MEMBER
1 POST

Common problem with Protoge, the alternator regulator is driven by the system computer located under the floor board at passenger side, lift the carpet and there is a metal plate remove it and turn it around the ECM a metal box with approximately 50 pin connector remove it and clean the contacts and pins with a contact cleaner (wear a ground strap). Also, in the fuse box located by the driver side fender in the engine compartment remove the top connector four nuts and the battery connections and flip it over there is an orange connector with a slide type of release lever if the terminals are darken by overheating also clean them really good with electric contact cleaner and a soft brush 99% of the time this would be your problem.
Who would of thought ECM controlled alternator output! This fixed my problem but it took me a week and two alternators before I realized that my Haynes manual did not included this darn circuit on its schematic diagram. Good luck!

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Tuesday, May 29th, 2012 AT 6:43 PM

RIVERMIKERAT

MECHANIC
6,110 POSTS

I always tell customers to start checking for bad connections, especially grounds, when something like this occurs. 99.9% of the time, they are the cause. Thanks for the heads up El Dongo.

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Saturday, July 28th, 2012 AT 6:24 PM