Duramax 6.6L L5P V8
Horsepower
445–470 hp
Torque
910–975 lb-ft
Years produced
2017–2026
Aspiration
Turbocharged
- Configuration
- V8, 6.6 L
- Aspiration
- Turbocharged
- Builder
- DMAX Ltd.
- Designers
- Joint venture of GM and Isuzu (DMAX); engine blocks supplied by Fritz Winter
- Years
- 2017–2026
Offered in: Chevrolet Chevrolet Silverado 2500HD, Chevrolet Chevrolet Silverado 3500, GMC GMC Sierra 2500HD, GMC GMC Sierra 3500
The L5P is the current Duramax, launched for 2017 at 445 hp and 910 lb-ft and described as GM's most powerful diesel when introduced. It carries through the K2XX and T1 trucks, with a six-speed Allison at first and a ten-speed Allison from 2020. For 2024 GM raised ratings to 470 hp and 975 lb-ft. The design is reported to handle far more output than its stock rating.
What made it successful
It combined large power and torque gains with a long production run, so parts and service knowledge are broad.
Market position
Its ratings were at or near the top of the class at launch. Sourced comparisons with Ford and Ram are not yet included.
Rebuild Potential
Tier BEditorial opinion.
The L5P's strongest point for a long-term keeper is its fuel system: GM dropped the Bosch CP4.2 used on the LML and fitted a Denso HP4 pump, which does not carry the CP4's failure record. Parts supply and the performance aftermarket are both deep. What holds it at tier B is age and complexity rather than any single flaw. GM's own bulletins for this engine are dominated by emissions and cooling work, not by bottom-end trouble, and because the engine is recent there is far less high-mileage teardown and independent machine-shop experience behind it than behind an LBZ or an older Duramax. Buy one to run and maintain, not as a cheap core to rebuild.
Best year ranges
- 2019-2026: GM's own coolant-leak bulletin (18-NA-098) and the 2017-2018 NOx sensor bulletin (17-NA-219) concentrate on the first two model years, so later trucks start with fewer of the documented early faults. This is an inference from bulletin coverage, not a GM statement that later years are better built.
Known weak points
Coolant leaks, coolant consumption and low-coolant messages. GM bulletin 18-NA-098 (2017-2021 6.6L diesel) maps the leak paths: cylinder head core hole plugs, block heater, cup plugs in the block, coolant hose and clamp, thermostat housing seal, and the bypass pipe O-ring and flange gasket.
Common fix: Identify which of the documented paths is leaking before replacing parts, then reseal or replace that component.
DEF and NOx aftertreatment faults. GM bulletin 17-NA-393 covers a 'poor DEF quality' message on the driver information center, and 17-NA-219 covers a lit MIL with auto stop inoperative on 2017-2018 trucks, including moisture intrusion past a damaged NOx sensor connector seal.
Common fix: Use fresh, properly stored DEF, and repair sensor and connector faults with compliant replacement parts rather than clearing codes.
Turbocharger boost control position fault. GM bulletin 21-NA-113 describes DTC P0046 set during engine crank, caused by a low-voltage condition during cranking that stops the turbocharger actuator learn from completing.
Common fix: Correct the battery and charging condition first, then let the actuator learn complete as the bulletin directs; the actuator is not always at fault.
Common upgrade categories
- Cooling system service and updated seals
- DEF and NOx sensor service with compliant parts
- Fuel filtration
- Transmission cooling and service parts
- Bolt-on intake and exhaust within local legal limits
This engine is emissions-equipped (EGR, particulate filter and DEF/SCR). Keep the emissions equipment the truck was built with and repair or replace it with compliant parts. Removing or defeating it on a vehicle originally equipped with it is illegal under federal law. Rules vary by state (for example California/CARB), so check local law and model-year requirements before modifying.
Sources
- Duramax V8 engine (Wikipedia) (accessed 2026-09-18)
- Chevrolet Silverado HD (Wikipedia) (accessed 2026-09-18)