2000 Mazda Protege 4 cyl Two Wheel Drive Automatic 90000 miles
My battery light was on and I was told I had a bad alternator. I switched it out and everything seemed Ok and the light went off. Two days later the light comes back on. I take it to the shop where I purchaed the alternator and they test it while the vehicle is on and they say they can't 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 don't 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 info.
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 underhood 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.
May, 29, 2012 AT 6:43 PM
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 arround the ECM a metal box with aprox 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 4 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 it tought. ECM controlled alternator output! This fixed my problem but it took me a week and two alternators before I relized that my Haynes manual did not included this darn circuit on it's schematic diagram. Good luck!
July, 28, 2012 AT 6:24 PM
I always tell customers to start checking for bad connections, especially grounds, when something like this occurs. 99.9% of the time, they're the cause. Thanks for the heads up El Dongo