GM has issued a service update for certain 2024 and 2025 GMC Sierra HD units that have been found to have sediment present in their transmission fluid, with a field action available to fix the problem.
The affected GMC Sierra HD trucks generate the sediment during the Output Shaft bearing press, according to Service Update number N242455950.
Before starting work on a potentially affected GMC Sierra HD unit, dealer service personnel should verify its involvement by checking the GM Global Warranty Management system to see if it is marked “Open.” Notably, the fix should be applied to all 2024 GMC Sierra HD and 2025 Sierra HD trucks brought to the dealership by customers for other service, as well as any affected units in inventory before those units are sold or delivered.
The remedy for the transmission sediment issue is to replace the transmission filter and all 15 quarts of transmission fluid in the truck. This process will take 90 minutes to approximately 2 hours, 15 minutes depending on the specific engine in the vehicle. The fix is available free of charge through the end of the pickup’s New Vehicle Limited Warranty period.
As a reminder, the 2024 model year debuted a mid-cycle refresh for the truck. The 2025 model introduces a few updates and changes, including availability of the Universal Vehicle Module (RPO code KGU) as on option for all Sierra HD trims so upfitters can add custom functions. The Adaptive Cruise Control with Trailering (RPO code KSG) becomes standard on four trim levels, up from two, and optional on the rest.
When it comes to motivation, the refreshed Sierra HD has a choice of two powerplants, the naturally aspirated 6.6L V8 L8T gasoline engine developing 401 horsepower and 464 pound-feet of torque and the 6.6L V8 L5P turbodiesel Duramax engine rated at 470 horsepower and 975 pound-feet of torque.
The Sierra HD rides on the GM T1 platform for both model years. The pickup continues to roll exclusively off the assembly line at a single facility, the GM Flint plant in Michigan.
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