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Did you let it run for awhile or take it for a drive?
Since the battery was disconnected for a good period of time, the PCM reset the fuel trims and they need time to relearn (usually a couple drive cycles).
Also, did you measure ~14.4V from the alternator while the car was running
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Make sure that your connection to the Mass Airflow sensor is still hooked up. If the MAF isn't reporting any voltage to the PCM it will trigger a battery light and a check engine light. The car will still idle as it will assume there is 8 grams of air incoming and apply the appropriate amount of fuel.
I'm having a similar problem. I replaced the battery and new alt.; not rebuilt, and the battery light stays on. The CEL came on a few days ago so I took it to the dealer today. They reset the PCM, and the CEL went out but the bat. light is still on and they have no idea why. The charging system checks out ok.
Did they get a code for the CEL? Or just reset it and hope it doesn't happen again?
On the alternator... The alternator light (mislabeled BAT on too many cars) essentially goes on when current flows from the battery to the alternator instead of from the alternator to the battery. I don't know if today's alternators are like this, but some time ago I had a car where the charging system functioned perfectly OK but the alt light was always on. Besides the main output diodes, there was a small "diode trio" kind of on the back side that got into the act. The dealer replaced that once during the one year warranty, and a couple of years later I replaced it myself.
Anyway, it needs someone who understands the electrical system, not just someone trained to put a tester on.
2006 MT, Galaxy Gray
Fuel cap hook
I'm not sure if they read a code or not, but I'd assume they did because the service writer said everything checked out. But their reason for me bringing it in was to reset the PCM, so maybe not. I'll have to ask next week when I take it back.
I'm really concerned that it may be fault in the ECU. I understand that is a costly repair!
Great point about finding a charging system expert, because you're right...some technicians only know what the readout tells them.
No code was displayed, so everyone was scratching their heads. I left it and they let it run with the test equipment on it for two hours and they said it stayed at 14.5 volts the entire time. When I got there the mechanic said, see nothing wrong like I said; look...I'll show you! So he turned it on and it read 10.0. More head scratching and stuttering. After swapping out the new alternator for another one, the battery/alternator light went out. Problem solved.