2015 Chevrolet Silverado 2500HD - P0401 EGR Flow Insufficient

Question

Got a P0401 code on my LML Duramax. The truck runs fine for the most part, maybe a little down on power when towing my 5th wheel, but the CEL won't stay off. I've cleared it three times and it usually returns after a day of mixed driving.

I'm at 145,000 miles and I do a lot of idling at job sites. I'm suspecting the EGR cooler is sooted up, but I'm hoping it's just a sensor. I don't see any leaks around the EGR valve itself. Anyone dealt with this on the LML specifically? I've heard the coolers on these are a pain to pull compared to the older LMM engines.

EmissionsEric · Accepted Answer

✅ Confirmed fix: The EGR cooler was almost 80% plugged with soot. Because of the excessive idling, the carbon buildup narrowed the passages so much that the differential pressure sensor didn't see enough flow.

I had to remove the EGR cooler assembly and soak it in a degreasing solvent for 24 hours, then pressure wash the internals. Once reinstalled with new gaskets, the flow rates returned to spec. If you do a lot of idling, you really need to run an additive or perform an Italian Tune-up occasionally to keep that soot from packing in.

WeldShopWanda · Answer

Before pulling the cooler, check the EGR position sensor map. Sometimes the valve itself gets 'lazy' and doesn't open as far as the ECM commands. You can usually command it open with a bidirectional tool to see if the commanded vs actual positions match up. If they don't, just replace the valve motor.

2015 Chevrolet Silverado 2500HD - P0401 EGR Flow Insufficient

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