DTC P0621 L61

The L-terminal circuit 225 is a two-way link between the PCM and generator. The PCM supplies the generator with 5 volts whenever the ignition is On. The PCM will not supply 5 volts to the generator during engine cranking if battery voltage is below 9.6 volts. Once the engine is running, the generator must have the 5 volt supply to charge. If the generator stops charging while the engine is running, it will ground this 5 volt supply from the PCM. When the PCM detects this ground, it will send a message to the I/P cluster over the Class II link to illuminate the Charge telltale.

DTC P0621 diagnostic runs continuously with ignition On.

P0621 is a (type D) DTC

With ignition On, engine Off, voltage measured with a DVOM on circuit 225 at the generator with the connector disconnected should read 5 volts.

A generator that is not charging with engine running will pull circuit 225 (through resistance) to ground and set this DTC.

An intermittent open or short to ground on circuit 225 will set this DTC. GENERATOR F-TERMINAL DC on the scan tool will read 0% with ignition On if this occurs.

GENERATOR F-TERMINAL DC on the scan tool should read near 17% with ignition On and engine Off.

DTC P0621 L81

The L-terminal circuit 225 is the link between the ECM and the 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 volt supply to charge. If the engine is not running or the generator stops charging while the engine is running, it will ground this 12 volt 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 P0621 will set if generator L-terminal input voltage at the ECM is greater than 4.0 volts when:

DTC P0621 diagnostic runs continuously with ignition On and engine Off.

DTC P0621 is a type D DTC.

With the 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 circuit 225 exists. If this occurs, the generator will stop charging.