Transmission Fluid Level Check 2025 GMC Sierra 3500 HD Denali 6.6L V8

The engine in your 2025 GMC Sierra 3500 HD should be running when you perform a transmission fluid level check, otherwise it will be inaccurate. The video above shows where the transmission fluid dipstick or the transmission fluid check plug is located in your Sierra 3500 HD and how to check the transmission fluid level. Your Sierra 3500 HD will have either a transmission dipstick or a check or fill plug to perform a transmission fluid check. The transmission dipstick will typically be in the engine bay or on top or even the side of your Sierra 3500 HD transmission. The transmission check plug will typically be on the bottom or the side of the transmission and may also be next to the axle. If the transmission fluid level in your Sierra 3500 HD is low, you need to add transmission fluid through the dipstick tube or the check plug hole. When adding transmission fluid to your Sierra 3500 HD, be sure to add it slowly as it will fill up quickly and is difficult to remove excess fluid if you overfill.

If you are having problems with the transmission in your Sierra 3500 HD, such as clunky shifting or hesitation, check the fluid level first - it is amazing how many drivers pay thousands of dollars for transmission work when a half quart of transmission fluid would have fixed the problem.