This is due to a faulty pcm. The voltage is regulated by the pcm itself. These fault codes indicate that the pcm is no longer properly regulating voltage to alternator and will need to be replaced
The pcm is the powertrain control module(on-board computer):
Fig. Fig. 18: The PCM is mounted on the inner left-hand fender, next to the battery
Fig. Fig. 22: As with the PM, first detach the air inlet hose from the computer housing to remove the PCM
Fig. Fig. 23: After removing the battery and tray, loosen the center bolt from the 60-way harness connector
Fig. Fig. 24: Pull the 60-way connector out of the PCM and make sure all of the connector holes are clean
Fig. Fig. 25: Loosen and remove the mounting screws from the PCM ...
Fig. Fig. 26: ... then lift the PCM out of the engine bay-1988-95 models