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Recipe - Duramax 6.6L V8 Turbo Diesel (GM HD, L5P 2017+ generation)

Specific Fix build

Reliability tier: aggregated - verify before ordering, see /disclosure/

DEF subsystem repair for the L5P (mode DEF system failures: tank heater, dosing, quality (L5P)): the emissions DEF hardware fails ahead of the engine - heater elements short or open (the VOQ signal clusters here), tank harnesses chafe, doser injectors crystallize. Work the cheap electrics first (harness, module), the doser second, the tank assembly last; and separate DEF-quality/level-sensor faults from real pump faults before ordering.

Parts

• Duramax L5P DEF Tank Harness 2020-2022 (OEM) - tank harness - the chafe/short that mimics every other DEF fault (qty 1)
• Duramax L5P DEF Controller (OEM) - DEF control module - the cheap brain before the expensive hardware (qty 1)
• Duramax L5P DEF Dosing Injector, pre-2021 doser (2017-2021) (OEM) - DEF dosing injector, pre-2021 doser (2017-2021) (12743094) (qty 1)
• Duramax L5P DEF Doser Injector 2021-2024 (OEM) - DEF dosing injector, 2021-2024 split (12696018) - confirm your build date, the doser changed mid-run (qty 1)
• Duramax L5P DEF Tank Assembly (OEM) - full tank assembly (heater+level/quality sensors) when elements test open (qty 1)

Install order

1. read codes and isolate: heater-element opens vs dosing-pressure faults vs level/quality sensor lies
2. harness and module first - cheapest fixes with the highest false-fault rate
3. doser injector: crystallized -> renew with the year-correct PN (2020/2021 split)
4. tank assembly only when heater elements or sensors test bad; fill fresh sealed DEF

Expected outcome

DEF dosing in spec, no heater codes, no countdown timers.

Do not

• do not buy the tank assembly on the first DEF code - the harness and module generate most of the fault traffic

Parts budget

About $70-$370 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.

• about $70: Duramax L5P DEF Tank Harness 2020-2022 (OEM) (about $70)
• about $110: Duramax L5P DEF Controller (OEM) (about $110)
• about $150: Duramax L5P DEF Dosing Injector, pre-2021 doser (2017-2021) (OEM) (about $150)
• about $75: Duramax L5P DEF Doser Injector 2021-2024 (OEM) (about $75)
• about $370: Duramax L5P DEF Tank Assembly (OEM) (about $370)

DIY or shop: Either: harness/module/injector are reachable; the tank assembly is a lift-or-crawl job.