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John
John, Master Automotive Technician
Category: Car
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Experience:  ASE A1-A8 & L1 Master GM Tech 40 years experience
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2001 6.6 DURAMAX DIESEL PO380 GLOW PLUG HEATER CIRCUIT PROBLEM NEW CONTROLLER NEW GLOW PLUGS ANY ADVICE ON THIS ONE

Hello RODNEY,

Have you looked at this :

Following published diagnostics for 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.

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Customer: replied 8 years ago.
175amp fuse ok. new controller, 8 new glow plugs, any other ideas.

Take a look at the G104 & 2 fuseable links on ckt 986 & 506,here is a schematic.

Object Number: 743064  Size: FS

Customer: replied 8 years ago.
circuits ok
If the circuits are good,I would have to say you have a bad ECM or connection.
Customer: replied 8 years ago.
CHECKED ONE MORE THING. ON GLOW PLUG CONTROLLER CICUIT 506 LT BLUE WIRE. CHECKED AT STUD ON CONTROLLER FOR 12VOLTS WHEN COMMANDING CONTROLLER ON AND OFF NO VOLTAGE. ON CIRCUIT 986 I HAVE 12 VOLTS. WHEN COMANDING GLOW PLUGS ON AND OFF. POSSIBLE NEW CONTROLLER BAD?
That is a possibility ,but check this first.With power from 175 amp fuse ckt 986 is energized by ECM thru ckt 985-purple/IA relay heater control.Ckt 506 is energized from ckt 505 yellow/pnk-yel from ECM glow plug relay control.Make sure ckt 505 is comming alive from ECM when you command glow plugs on.
Customer: replied 8 years ago.
circuit 505 is coming alive when you command glow plugs on. must be faulty controller? i think we have check every thing else?
At this point I believe you are right.
Customer: replied 8 years ago.
THANKS FOR YOUR HELP!!!!!

YOU ARE VERY WELCOME.Please come back again

John