Starting and Charging Diagnosis

Schematic:

CIRCUIT DESCRIPTION
The L-terminal circuit 225 is the link between the ECM and generator. The ECM supplies the generator with 12 volts whenever the ignition is On. Once the engine is running, the generator must have the 12 volts supply to charge. If the engine is NOT running or the generator stops charging while the engine is running, it will ground this 12 volts supply from the ECM. When the ECM detects this low voltage state, it will send a message to the BCM over the CAN link, which will send a message to the I/P cluster over the Class II link to illuminate the Charge telltale. DTC P0621 will set if the voltage at the generator L-terminal input is high when the engine is NOT running.

DTC PARAMETERS
DTC P0621 will set if generator L-terminal input voltage at the ECM is greater than 4.0 volts when:
^ Condition exists for longer than 3 seconds
^ Engine is NOT running
^ Ignition is On
DTC P0621 diagnostic runs continuously with ignition On and engine Off.
P0621 is a (type D) DTC.

DIAGNOSTIC AIDS
With ignition On, engine Off, voltage measured with a DVOM on circuit 225 at the generator with the ring terminal disconnected should read battery voltage. With the ring terminal connected, voltage should be between 1.0-1.6 volts.

An intermittent open or short to voltage on circuit 225 will Set this DTC.

To locate an intermittent problem, use Scan tool to monitor IGNITION 1 voltage. Wiggling wires with engine running may locate the area where an open in circuit 225 exists. If this occurs, the generator will stop charging.

TEST

Diagnostic Chart: