2012 Isx 2350 475 with codes 4726 and 0559

[ahrenbenjudah]

One of my drivers reported truck was running a little rough. I looked at the codes remotely and had the following: 1 count of 4726 active and 2 counts of 0559 inactive. He made it back to the yard and this morning the truck will now crank but not start.

I scanned it and while looking at the data, with key on/engine off, the commanded fuel pressure is 5500 (approximately) but actual fp is <200. And the fuel pressure rationality sensor reads -1100ish. To be completely honest I have no idea what a fuel pressure rationality sensor is.

Anyways. I’ve had a similar situation before and I just tossed a pressure relief valve on there and it solved the issue. So I did the same here but it didn’t change anything. I figured my next step would be trying leakdown tests, but I figured I would have an injector code too if that was the issue but I don’t.

If I crank the engine, it doesn’t build any pressure (based on readings on insite). Either that or it does but bleeds back off immediately. When I just turn the key over, the lift pump activates, but I haven’t tested if it’s putting any pressure out yet.

Just looking for some ideas before I dive in to it again on Monday.

I also have a couple after treatment codes but it appears they stem from the fueling issue stopping regens from happening.