2001 GMC Sierra glow plug circuit code0380

Need more info, is this a no start condition?Is this federal or california emissions?This makes a difference in diagnosis. For now you can follow this info, DTC P0380, P0621 or a no charge condition may lead to unnecessary generator or ECM replacement. You should first check the 175-amp battery fuse. If the 175-amp battery fuse OR circuit 506 is open, no voltage will be present on circuit 506 at the PCM. This will cause the P0380 to set. The ECM monitors the glow plug signal using circuit 506. The ECM expects to see battery voltage on circuit 506 when the glow plugs are commanded on. If no voltage is present on circuit 506, the ECM will stop sending the turn on voltage to the generator L terminal circuit 25, causing the no charge condition and the P0621 to set. Post back with what you find.