DTC P0620: Generator Performance: Description

Powertrain Control Module (PCM) uses generator turn on signal circuit to control generator. A high side driver within PCM allows PCM to turn generator on and off. When generator operation is desired, PCM sends a 5-volt signal to voltage regulator via generator turn on signal circuit. This causes voltage regulator to begin controlling generator field circuit. Once generator is enabled by PCM, voltage regulator controls generator output independently of PCM. Under certain operating conditions, PCM can turn off generator by turning off 5-volt signal on generator turn on signal circuit. PCM has fault detection circuitry which monitors state of generator turn on signal circuit. DTC sets when fault detection circuit senses a voltage other than what is expected. Voltage regulator also contains fault detection circuitry. If regulator detects a problem, regulator will ground generator turn on signal circuit, pulling voltage low. This also causes PCM to set the DTC.

PCM receives generator output feedback via generator field duty cycle signal circuit. Voltage regulator generates a PWM signal on field control circuit. Regulator varies pulse width of this signal in order to control generator output. This signal is also sent to PCM via generator field duty cycle signal circuit. Pulse width of signal is proportional to generator output. PCM expects generator output to be within a predetermined range under certain operating conditions. DTC sets when PCM detects PWM signal on generator field duty cycle signal circuit is not within expected range. When this DTC sets, the PCM sends a class 2 serial data message to the Instrument Panel (IP) illuminating the charge indicator light.