P1637 GMC - Generator L-Terminal Circuit
- Generator harness is open or shorted
- Generator circuit poor electrical connection
- Powertrain Control Module (PCM) programming
- Faulty PCM
The L-terminal circuit from the generator is a discrete circuit (a discrete circuit has no splices and only one source and one destination) into the Powertrain Control Module (PCM). The PCM applies ignition voltage to the generator L terminal circuit. A small amount of current flows from this circuit through the generator windings to create a magnetic field which starts the generator process. When the generator is at operating speed and producing voltage, a solid state switch for the L terminal circuit in the generator opens and the PCM detects that the initial startup current flow has stopped.
The PCM expects to detect low voltage on the L terminal circuit prior to the generator rotating at operating speed and conversely expects the circuit to be at ignition voltage potential when the generator is operational.
Any information is appreciated. Thanks