P1637 GMC - Generator L-Terminal Circuit
- Faulty Generator (Alternator)
- Generator harness is open or shorted
- Generator circuit poor electrical connection
- Powertrain Control Module (PCM) programming
- Faulty Powertrain Control Module (PCM)
When is the code detected?
- Engine Light ON (or Service Engine Soon Warning Light)
P1637 Gmc Description
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.