Battery light in ford focus 2002

why is my battery light still on? i changed the alternator and had the battery tested?

Are both parts OK? If so, the problem is in electrical connections somewhere. Good luck and please let us know what you find.

Your car uses a powertrain computer algorithm to control the charging system. It commands the alternator, as well gets information from the alternator using the Gencom & Genmon communication ports. There’s also involvement wth the igntion switch and the SCM communication port between the PCM and the instrument cluster (where the battery warning light is located). The instrument panel computer turns the warning light on when the key is turned to “on”, and it is the PCM’s responsibility to command the instrument panel computer to turn it off if it has determined that the charging system is working correctly. What I guess all this means for you ,is that the best path at this point is to take the vehicle to a shop that has access to a computer scanner which can monitor all of the above digital buss transactions to see where in the chain something is failing. My guess is that either the PCM isn’t able to properly communicated with the instrument cluster for some reason, or that the new alternator isn’t working.

If you know how to measure voltages, one test that’s pretty easy: Before first start of the day the battery should measure about 12.6 volts. Then immediately after starting the engine, 13.5 -15.5 volts. What do you or your shop measure?

BTW, you’ll probably get better results here by posting this in maintenance/repair section of the forum. Click “the show” above left, then “maintenance repair”, then “new topic” above right.

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