General Information

Engine Control
P0620 Alternator Control Circuit - General Information

Component Location





General Description

The alternator management system controls the charging voltage output to improve fuel economy, manage alternator load under various operating conditions, keep the battery charged, and protect the battery from over-charging. The PCM controls the output voltage by using a duty cycle (charging control, discharging control, normal control) based on the battery conditions and vehicle operating conditions. It is important to have a stable power supply, so a battery sensor is part of the charging system. The Battery sensor is mounted on battery (-) terminal. It transmits battery voltage, current and temperature information to the PCM. The PCM controls output voltage by increasing or decreasing the duty cycle on the COM circuit to the alternator based on these signals.

DTC Description

If the COM circuit from the alternator to the PCM is open or shorted, the PCM sets a P0620 DTC.

DTC Detecting Condition





Diagnostic Circuit Diagram





Signal Waveform & Data








Fig.1) Normal waveforms of COM, FR terminal of alternator at idle.
Fig.2) Normal waveforms of COM, FR terminal of alternator under high electronic load condition
- When the eletronic load (head lamp, room lmap. ) is applied, the duty(+) value of the FR line is increased.