Powertrain Diagnosis

Diagnostic Chart:

Schematic:

The ECM continuously monitors the signal from the generator. If the ECM detects an open circuit on the generator circuit, this code will set.

DTC PARAMETERS
This DTC will set when:
^ ECM detects an open circuit
^ Engine Speed greater than 40 rpm

DTC P0621 is a (type D) DTC.

DIAGNOSTIC AIDS
To locate an intermittent problem, use the Scan tool to monitor ignition 1 voltage with engine running.

Wiggling wires while monitoring ignition 1 voltage may locate when an open exist.

IMPORTANT: An open L-terminal circuit will cause the generator not to charge below 2500 engine rpm. Above 2500 rpm, the generator will self excite its field windings and begin to charge.