Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P0620: Fault Detection Circuit Malfunction (Century, Grand PRIX, Intrigue & Regal): 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. If fault detection circuit senses a voltage other than what is expected, this DTC will set. 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 DTC. PCM receives generator output (electrical load) 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. If PCM detects that PWM signal on generator field duty cycle signal circuit is not within expected range, this DTC will set. When this DTC sets, PCM sends a class 2 serial data message to IPC illuminating Charge indicator light.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.