6.6L Duramax L5P Platform

2017-2023 L5P Duramax

Here is a brief overview of the L5P platform.

The 6.6L L5P is the latest RPO in Chevy/GMs line of Duramax Diesels. The L5P came to the market in 2017 and is still in production in 2024. The L5Ps have one of the more complicated emissions systems including Selective Catalytic Reduction (SCR), Diesel Oxidation Catalyst (DOC), Exhaust Gas Recirculation (EGR), Diesel Particulate Filter (DPF), and Diesel Exhaust Fluid (DEF). Although there have been steps made to improve the function of these systems, they can still be very problematic, and difficult to get parts for when something fails. 

The platform used for the L5Ps is HP Tuners. It uses a physical file that the tuners made from the stock file read directly from you vehicle after the ECM is unlocked. For a long time, unlocking the ECM required sending your stock ECM in to be unlocked by HP Tuners, which caused a lot of vehicle downtime, or you had to purchase an already unlocked ECM, which was expensive. Hp Tuner has now designed an unlock cable that allows you to unlock your stock ECM with it still in the vehicle. This has really helped to reduce the downtime, and cost of tuning.

With just a tune, they are capable or making roughly 600 rwhp. For additional power, the first upgrade needed is a bigger turbo. The L5P was the first to offer the ability to switch tunes on the fly using the cruise control buttons on the steering wheel with HP Tuners operating system. This eliminates the need to install a switch that pins into the ECM harness, or drill a hole in the dash to mount it like the earlier year Duramax’s. There is also the option to get a single power level of your choice. Tuning is currently only available up to the 2023 version of the truck as the Global B ECM in the 2024 has not yet been unlocked. 

Transmission tuning is available for all years of the L5P excluding 2024. The 2017-2019s have a 6 speed Allison Transmission, and the 2020-2023s have moved to a 10 speed Allison Transmission. Both offer transmission tuning that can adjust line pressure, shift pattern and timing, and torque converter lockup schedule. It helps to increase the holding capacity of the transmission, as well as match the shift pattern and torque converter lockup schedule to the new torque curve of the ECM tuning.