2019 GMC Sierra 1500 Transmission Fluid & Service

Quick answer

• Transmission Make/Model: GM 8L90 or GM 8L45 (depending on engine/configuration)
• OEM Fluid Spec: DEXRON HP (for 8L90 & 8L45)
• Drain & Fill Capacity: ~7-8 quarts (8L90 & 8L45, fluid level dependent on temperature)
• Full Overhaul Capacity: ~12.4 quarts (8L90) / ~9.7 quarts (8L45)
• Filter OEM Part Number: Verify with dealer or service manual (different for 8L90 vs 8L45)
• Recommended Service Interval: 97,500 miles (normal duty) / 45,000 miles (severe duty/towing)

Fluid type explained

The 2019 GMC Sierra 1500 can come equipped with either the GM 8L90 (paired with the 6.2L EcoTec3 V8 L87 engine) or the GM 8L45 (paired with smaller engines like the 5.3L EcoTec3 V8 L84 or the 4.3L EcoTec3 V6 LV3). Both of these advanced 8-speed automatic transmissions utilize a specific proprietary fluid: DEXRON HP. It is crucial to use only DEXRON HP fluid when servicing these transmissions. Using any other fluid, even those labeled as multi-vehicle or compatible with DEXRON VI, can lead to premature wear, poor shifting, and potential transmission failure. DEXRON HP is engineered to meet the demanding requirements of these modern transmissions, providing optimal friction characteristics, wear protection, and thermal stability across a wide range of operating temperatures.

Always double-check your owner's manual or consult with a GM dealership to confirm the exact fluid specification for your specific Sierra 1500 configuration. While DEXRON HP is the correct fluid, verifying ensures you are using the right product for your vehicle.

Service procedure

Servicing the transmission fluid on a 2019 GMC Sierra 1500 can involve a simple drain and fill or a more comprehensive full fluid exchange. Due to the complexity of modern transmissions like the 8L90 and 8L45, and the critical importance of exact fluid levels and temperatures, a DIY approach can be challenging and is generally not recommended unless you have significant automotive experience and specialized tools.

Drain & Fill: This method involves draining the fluid from the transmission pan and refilling it with new fluid. This typically replaces only a portion of the total fluid volume, as a significant amount remains in the torque converter, valve body, and cooler lines. For the 8L90 and 8L45, a drain and fill will replace approximately 7-8 quarts of fluid. This can be a viable option for routine maintenance when performed at recommended intervals.

Full Fluid Exchange: A full fluid exchange (also known as a flush) involves using a specialized machine to circulate new fluid through the transmission system, pushing out all the old fluid. This method replaces nearly 100% of the transmission fluid, including what's in the torque converter and cooler lines. While more thorough, it's important that this procedure is performed correctly by experienced technicians to avoid potential damage, especially if the old fluid is severely burnt or contaminated. For the 8L90, the full overhaul capacity is approximately 12.4 quarts, and for the 8L45, it is about 9.7 quarts.

Regardless of the method, accurate fluid level checking is critical. These transmissions have a specific procedure for checking the fluid level, often involving a dipstick-less design and requiring the transmission to be at a specific operating temperature range. Overfilling or underfilling can lead to transmission problems.

When performing any service, the transmission filter should also be replaced. The specific filter part number will vary between the 8L90 and 8L45 transmissions. Always verify the correct part number with your GM dealer or service manual.

Service interval

Maintaining the correct transmission fluid and adhering to recommended service intervals is paramount for the longevity and performance of your 2019 GMC Sierra 1500's transmission.

• Normal Duty: For vehicles operating under normal driving conditions (e.g., no heavy towing, extreme temperatures, or frequent stop-and-go traffic), the recommended transmission fluid and filter service interval is every 97,500 miles.

• Severe Duty / Towing: If your Sierra 1500 is frequently used for towing, hauling heavy loads, driving in mountainous terrain, or experiences consistent stop-and-go traffic or extreme temperatures, it falls under severe duty conditions. In such cases, the transmission fluid and filter should be serviced much more frequently, typically every 45,000 miles.

Skipping transmission fluid changes can lead to fluid degradation, increased wear on internal components, and ultimately, premature transmission failure. The advanced nature of the 8L90 and 8L45 transmissions means they are particularly sensitive to fluid quality and level.

Common transmission problems

While the GM 8L90 and 8L45 transmissions are generally robust, like any mechanical component, they can experience specific issues, particularly in their earlier generations. For the 2019 model year, some common concerns reported by owners can include: