96 Regal GS Battery light comes on after driving

After some recent repairs; new PCM and upper intake, cleaning of throttle body, the battery light comes on after driving about half a mile. The car starts fine and the lights are bright and charging is ok. It's almost like it's backwards from normal oeration where battery light comes on during start then goes off. Any ideas?

Check the belt and tensioner. This sounds like the belt is slipping on the alternator due to lack of tension. The tensioners do go bad and can cause this issue. Also check the wire at the alternator to make sure it is clean a bad connection can cause charging issues. Finally check and clean the battery terminals and check the grounds.

Thank you for your reply. I did just replace the tensioner pully and check the belt. It is odd because there seems to be no hint of low battery charge. Sequence is: Key on, battery light on; Start, car starts and battery light goes off with other indicator lights. However after about a mile of driving, the battery light comes on and stays on until the key is turned off. Then the sequence is repeated. As an aside, the low oil level now will not turn off until about the same time as the battery light comes on. Oil level is good. None of this occoured until the recent repairs. We replaced the PCM for low reference voltage to the MAP sensor. I almost wonder if we got a defective PCM.

Thank you for your reply. I did just replace the tensioner pully and check the belt. It is odd because there seems to be no hint of low battery charge. Sequence is: Key on, battery light on; Start, car starts and battery light goes off with other indicator lights. However after about a mile of driving, the battery light comes on and stays on until the key is turned off. Then the sequence is repeated. As an aside, the low oil level now will not turn off until about the same time as the battery light comes on. Oil level is good. None of this occoured until the recent repairs. We replaced the PCM for low reference voltage to the MAP sensor. I almost wonder if we got a defective PCM.

The PCM monitors the charging system output from the alternator and if abnormal will trigger the light so that is a possibility and especially if you did not have the problem before the PCM replacement.

Thanks. I just called the tech and he is ordering another PCM.

Thanks. I just called the tech and he is ordering another PCM.

Good luck! and let us know how it turns out.

Well, new PCM and not fixed. Battery light came back on after about 2 miles combined street/hiway driving. The charge light fault began immediately following the last repair which was for intermittant low speed stalling. Included R&R PCM (low reference voltage), MAP sensor (cracked), and upper intake manifold (cracked at throttle body). Still has this but now sets a MAF code. I do know that while the car was in the shop, the battery ran down due to underhood light being left on. Could this have been as simple as a battery?

Well, new PCM and not fixed. Battery light came back on after about 2 miles combined street/hiway driving. The charge light fault began immediately following the last repair which was for intermittant low speed stalling. Included R&R PCM (low reference voltage), MAP sensor (cracked), and upper intake manifold (cracked at throttle body). Still has this but now sets a MAF code. I do know that while the car was in the shop, the battery ran down due to underhood light being left on. Could this have been as simple as a battery?

Sorry to hear that. Have you checked the static voltage across the battery pos. & neg. terminal for around 12v. Engine off. With engine running you should see around 14 - 15 volts and no greater than 17 volts. Also, how is the connector at the alternator...any corrosion? For the PCM to operate properly it must have good voltage (PCM sense) and a good ground. You might consider getting the battery tested like at Autozone. There is no charge. They can test the alternator too. Good luck!