Recipe - GM 3.0L Duramax LM2/LZ0 I6 (2020+)
Specific Fix build
Reliability tier: verified - verify before ordering, see /disclosure/
EGR cooler / valve job for the 3.0L Duramax (mode EGR system failures: valve, cooler, wiring (derate-prone)): rarely named in NHTSA complaints (8 of 1,190) but forum-documented - recurring 'Service Emission System' with the 65-mph derate. Split the fault: electrical (valve, harness) fails without coolant loss; the cooler shows as slow coolant loss with no puddle, sometimes white smoke on cold start. Do the valve while the cooler is out - the labor overlaps.
Parts
- 3.0L Duramax EGR Cooler (GM 55513487) - the cooler (55513487) - the internal-leak item when coolant drops (qty 1)
- 3.0L Duramax EGR Valve, low-pressure circuit (GM 55510254) - low-pressure EGR valve (55510254) - replace while the circuit is open (qty 1)
- 3.0L Duramax EGR Valve, high-pressure circuit (GM 55510043) - high-pressure EGR valve (55510043), 2020-2023 circuit (qty 1)
- 3.0L Duramax EGR Valve, LZ0 high-pressure circuit 2023-2024 (GM 40009269) - LZ0 high-pressure valve (40009269) for 2023-2024 pickups (qty 1)
Install order
- read codes: P2C7A / EGR position codes point electrical; coolant loss with no puddle points at the cooler (pressure-test first)
- verify the EGR wiring harness connector before parts - the electrical layer is repair work, no catalog part
- cooler out: replace, inspect the turbo coolant circuit while open (the circuits share the TSB MC-10165111 layout)
- valves while in there - match the valve to the circuit coded and the truck year (LP/HP/LZ0 split)
- refill, bleed, drive cycle, confirm the derate lifts
Expected outcome
Parts budget
About $75-$250 in parts. It depends on what the diagnosis finds; each option below is what you buy together. Prices marked "at Dave's" are Dave's Auto Center's, the same as in his store; the others are approximate prices from OEM and maker catalogs, rounded (a manufacturer's list price can run higher). Parts only, no labor.