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P0683 = glow plug diagnostic signal communication fault
P1280 = ICP circuit out of range low
You should be looking to pull the IPR and check it for obstruction or blown o-ring inside. Gonna make a mess when you pull it unless you have a bottle cork to stick in the hole it comes out of. Several diesel shops make a rubber plug to jam in there when pulling the IPR so all the oil in the HPOP reservoir doesn't flow out into the engine valley. You can rebuild the IPR or buy a new one, but it looks to me (from the good description you gave of the circumstances) that it is your problem. I doubt it is your pump, but there are very low odds it could be.
There are two o-rings, but the one close to the end is critical to proper function under high pressure. the IPR comes apart (unscrews) and can be cleaned of debris internally
cork I bought that works great to plug the hole. Got it at Lowes in the hardware section.
You will need one of these as deep as you can find. this one is just over 3 inches long and works great.
Drill out the base with a bit the same size as the IPR shaft. The drill bit I used was just small enough to not touch the square sides of the drive end.
Perfect fit and can still get the ratchet on the socket.
