Starting and Charging Diagnosis
Schematic:
DTC PARAMETERS
The ECM will set DTC P1637 if L-terminal voltage falls below a calibrated point with engine RPM > 40.
DTC PARAMETERS
The ECM monitors the generator signal continuously.
DTC P1637 is a type D code which will not illuminate the telltale.
Diagnose intermittent problems with Scan tool by monitoring ignition 1 voltage. Wiggling wires with engine running may identify an intermittent open circuit.
If the L-terminal circuit is open, the generator will not charge when engine speed is below 2500 rpm. Above 2500 rpm, the generator field windings will self excite and charge.
Diagnostic Chart:
