I have an 03 mazda 6 4cyl. Just put on new fuel pump like last week and coolant temp sensor. Put on new refurbished alternator and battery last night and yet still the battery light comes on. Why can anyone help me? This is the 5th battery and alternator in 3 years. The care is idling fine running smoother since the fuel pump was changed. It vibrates a little when the air kicks in but other than that its good.

Two days ago is when it started. Sunday we fixed the fuel pump and temp sensor. Ran great after. Monday around 3 battery light comes on. We ran two errands that night and by the time we got home it loss power and died. Had to get a jump and it died not even a mile away. Its running and starting up fine but can figure out why the light is on. We have had both the new battery and refurbished alternator checked at many different auto stores and they say its good and have no clue why the light is on. But they did say the alternator is running at 11.75 volts and needs 12-14. Any help would be great!

 

Did you change the belt?

 

No we did not change the belt. Since this post we noticed the pigtale connector to the alternators housing was corroded. The dealership doesnt sell this part alone. You have to purchase the whole harness. So instead we went to a local auto shop that also specializes in electrical and purchased a 90% similar housing with new wires. Put it on and everything ran smooth for 2 days. This morning the battery light came back on and off and on and off. We came to a stop and it went into safe mode and everything dimmed in the car. My boyfriend said to pull over and turn it off and restart it. It wouldnt start. Had to get a tow home. I seriously need some help. We can figure why?

 

Change the belt

 

FYI - The alternator in a Mazda 6 is controlled by the PCM/ECU.

I've had to replace a few ECU/PCM's in the past.

 

That puts questioning the pcm out imo. You've had the alternator off, change the belt, or check tension. If it is original, and stretched, this will cause the issue you have.