Alternator Functional Check: Notes

PCM supplies 12 volts to alternator terminal "L" and initiates alternator operation. The alternator regulator applies voltage to the rotor as a Pulse Width Modulated (PWM) signal to energize field windings. The regulator increases the duty cycle and controls the charging system voltage. The ampere rate of battery charge and power supplied to vehicle is also controlled. The regulator controls system voltage through internal voltage sensing.

A/C voltage is generated in the stator and changed to D/C voltage by 6 diodes in the rectifier bridge. If a diode is open, maximum amperage output of alternator will be reduced by 10 percent. If a diode is shorted, maximum output will be reduced by 30 percent. A shorted diode may cause Code P110 to set and the alternator may have a growling noise due to the electrical imbalance. Maximum alternator output will occur at 2000 RPM. At idle, output should be 30 percent of maximum output.

1. Always diagnose codes before performing the ALTERNATOR FUNCTIONAL CHECK . This step will test the PCM's ability to detect alternator faults and out of range voltage conditions.
2. Over-voltage conditions may be caused by a defective rotor or regulator. Overcharging may be evidenced by low electrolyte level in battery eye.
3. Insufficient amperage output may not set codes but result in marginal battery charging if driving habits involve short trips and prolonged idling, especially in warm weather. Low output may be caused by a defective regulator, an open or shorted diode, or contaminated brushes. No output condition may be caused by a defective regulator, an open or shorted rotor, damaged stator or brush wear.