Alternator / Generator Symptoms and Replacement

An alternator is the device that spins and generates current that is used to charge your battery.  It also provides power to run your lights and other electric accessories on your car while it is running. There is electronics to monitor and control the charging process. The Red Battery light on your dash board comes from this circuit and tells if you there is a malfunction of the charging circuit. Sometimes the light will not show all malfunctions. So if your battery is dead (or out of juice) and you don't remember keeping the light on or any such obvious reasons , it could men there is a problem with the charging system. The best way to find out the charging is ok is to connect a multimeter and measure the car battery voltage at rest with the key turned on , but car not started. Lets say it reads 11.7 volts now Then when you start the car the measure should go up , say to 13.5 Volts or similar. Basically the voltage should go up when the engine runs if it does not it suggests a problem.


Put a voltmeter across the battery while the engine is running . Voltage should be 14.2 volts. Lower than 14 volts or higher than 14.4 volts could mean an alternator problem. Turn on the lights and accessories: voltage should stay up around 13 volts. Idle engine up to 2000 RPM. Voltage should go up to 14 or so. (Testing numbers are for 12 volt systems)  IF THE VOLTAGE GOES UP TO 14.2 VOLTS YOU NEED NO ALTERNATOR REPAIR!

Because the alternator is mechanical device it is subject to mechanical issues as well , whose symptom is a noise Since the rotor is always spinning while the engine is running, there needs to be bearings to support the shaft and allow it to spin freely.  If one of those bearings were to fail, you will hear a grinding noise coming from the alternator.  A mechanic's stethoscope can be used to confirm which of the spinning components driven by the serpentine belt is making the noise.

All these things can be good and the car still is not able to charge, then it could mean a regulator, wiring cables or a fuse. Consult your repair manual for specific instructions to diagnose a regulator or to check relevant fuses or cables. You need to have a multimeter handy to follow these tests

Replacement :

In the event of a failed alternators , it can be repaired, but over here, it is not economical to do this. See here to find a replacement alternator. Normally alternator replacement is a good DIY repair project, with the following caution: DISCONNECT THE BATTERY GROUND CABLE!!! Here are the steps.

1.) Disconnect the Battery -ve(Black or Ground) Terminal

2.) Remove the Alternator belt. See the section on Serpentine Belt Replacement. Most serpentine belts have an automatic belt tesioner. You relieve the pressure either with a wrench on the tensioner pulley nut, or some have a square hole in them for either a 1/2 inch or 3/8 inch ratchet or breaker bar. IN ALL CASES remove the belt, then remove the alternator. The alternator is held on by 2 mount bolts and a 3rd guide bolt , all there have to be removed to drop the alternator. Carefully disconnect the wiring harness and terminals. Follow the reverse order to put in a  new alternator.

3.) Connect the Battery Terminal back now and then start the engine. Follow the testing with a voltmeter described above to make sure it is charging fine.