My AMP light came on the other day, so I connected my voltmeter to the battery which revealed 12.6 volts with the engine off. I then started the car and the voltmeter revealed 12.5 volts. I increased engine RPM to 2000 and the voltmeter still read 12.5 volts.
I removed the alternator belt, disconnected the negative battery terminal and gave the alternator pulley a spin. It spun freely. I then reconnected the negative battery terminal and the pulley spun, but not as freely as with the negative battery terminal disconnected. The pulley also does not spin freely when the ignition is in the 'ON" position. I once read that if the pulley spins freely with the key in the 'on' position, then it's either a faulty voltage regulator or the alternator brushes need replaced.
This is a 2G ( 2nd generation ) alternator. The voltage regulator is attached to the rear of the alternator & the brush holder is attached to the voltage regulator.
Could you tell me if this is could possibly be a faulty voltage regulator, or is it most likely a diode or stator issue? Should I replace the alternator?
Monday, June 1st, 2020 AT 2:17 PM