code 1637 is a generator l circuit code code 300 is a multiple misfire code. from what you are describing i would lean towards wiring problem with alternator circuit.
The L-terminal circuit from the generator is a discrete circuit into the Powertrain Control Module (PCM)
. The PCM supplies the ignition voltage to the generator lamp feed. This ignition voltage is pulled low by the generator once the ignition switch
supplies ignition 1 voltage
. The voltage stays low until the generator turns. When the generator is up and running, the PCM detects ignition voltage. Therefore, with no failures with the vehicles charging system, the lamp terminal circuit will go low 0 volts
when the ignition switch is powered up and then goes to the ignition voltage after the engine is started.
I find it hard to believe you need a third alternator. if you do something is going on to burn them up. have them check wires might have a harness rubbed thru grounding out at times