2019 Chevrolet Silverado 2500HD: Transmission Fluid & Service

Quick answer

• Transmission: Allison 1000 6-speed automatic (L5P Duramax diesel) or GM 6L90 6-speed automatic (6.0L Vortec V8 gas)
• OEM fluid spec:
  • Allison 1000: TES 668 / DEXRON VI
  • GM 6L90: DEXRON VI
• Drain & fill capacity:
  • Allison 1000: Approx. 7.4 quarts (6.9 liters)
  • GM 6L90: Approx. 6.3 quarts (6.0 liters)
• Full overhaul capacity:
  • Allison 1000: Approx. 12.7 quarts (12.0 liters)
  • GM 6L90: Approx. 12.4 quarts (11.7 liters)
• Filter OEM part number:
  • Allison 1000: GM Part #29542824 (Verify with dealer or service manual)
  • GM 6L90: GM Part #24252157 (Verify with dealer or service manual)
• Recommended service interval:
  • Normal duty: 45,000 miles (DEXRON VI) to 150,000 miles (TES 668)
  • Severe duty: 25,000 miles (DEXRON VI) to 75,000 miles (TES 668)

Fluid type explained

For the 2019 model year, Chevrolet equipped the Silverado 2500HD with two distinct six-speed automatic transmissions, depending on the engine choice. Gas-powered trucks with the 6.0L Vortec V8 received the GM 6L90 transmission, while trucks with the 6.6L Duramax L5P diesel engine were paired with the legendary Allison 1000.

The required fluid type is specific to the transmission. Both the 6L90 and the Allison 1000 are factory-filled with DEXRON VI automatic transmission fluid (ATF). However, for the Allison transmission, owners have the option to upgrade to a TES 668 specification fluid. TES 668 is a modern, full-synthetic fluid developed by Allison for high-performance and severe-duty applications. While DEXRON VI is perfectly acceptable, TES 668 offers superior thermal stability, oxidation resistance, and shear stability, which allows for significantly extended service intervals.

Using a fluid that does not meet the DEXRON VI or TES 668 (for Allison) specification can lead to poor shift quality, overheating, and premature transmission failure.

Service procedure

Properly servicing your Silverado's transmission is key to a long service life. There are two common methods for changing the transmission fluid:

• Drain and Fill: This is the most common and straightforward method. It involves removing the transmission pan's drain plug, allowing the old fluid to drain out, and refilling the transmission with new fluid. This process typically replaces about 60-70% of the total fluid in the system, as a significant amount of old fluid remains trapped in the torque converter, valve body, and cooler lines. For this reason, a drain and fill should be performed more frequently.

• Full Fluid Exchange: A full exchange or "flush" is performed using specialized equipment that connects to the transmission cooler lines. This machine pushes new fluid into the system while simultaneously extracting the old fluid. This process replaces nearly 100% of the old, degraded ATF. A full exchange is the most effective way to service the transmission but should only be performed by a qualified shop to prevent the risk of dislodging debris and causing damage.

During either service, it is critical to replace the transmission filter. The Allison 1000 features an external, spin-on filter that is easily accessible, while the GM 6L90 has an internal filter located inside the transmission pan, which must be removed for access.

Service interval

The recommended service interval depends heavily on how you use your truck. Chevrolet provides two schedules: normal duty and severe duty.

Severe duty applies to trucks that frequently:

• Tow heavy trailers or haul heavy loads
• Operate in heavy city traffic with high ambient temperatures
• Are used for commercial purposes (delivery, snow plowing)
• Are used for frequent off-road driving

For the Allison 1000:

• Normal Duty: Using a TES 668 fluid allows for an impressive 150,000-mile interval. If using standard DEXRON VI, the interval is 60,000 miles.
• Severe Duty: Allison recommends a 75,000-mile interval with TES 668 fluid. With DEXRON VI, this is shortened to just 30,000 miles.

For the GM 6L90:

• Normal Duty: The recommended interval is every 45,000 miles.
• Severe Duty: The interval is shortened to every 25,000 miles to protect against the increased heat and stress.

Common transmission problems

While generally reliable, both transmissions can experience issues, especially as they accumulate mileage or are subjected to heavy use.

Allison 1000 (L5P generation):

• Torque Converter Clutch (TCC) Shudder: Some owners report a shudder or vibration when the torque converter clutch applies, often felt at highway speeds. This can sometimes be addressed with a fluid exchange and a friction modifier additive, but may indicate a failing torque converter.
• Solenoid Failure: Though less common on later models, a failed pressure control or shift solenoid can cause erratic shifting, delayed engagement, or a check engine light.

GM 6L90:

• Torque Converter Issues: The 6L80/6L90 family is known for potential torque converter failures, which can present as a shudder, slipping, or complete loss of engagement. Debris from a failing converter can quickly contaminate the entire transmission, necessitating a full rebuild.
• Delayed Engagement: A delay when shifting from Park to Drive or Reverse can be an early sign of internal seal wear or low fluid pressure.
• Harsh Shifts: Hard or jerky shifts, particularly the 1-2 or 2-3 upshift, can point to issues within the valve body or with the transmission control module (TCM) tuning.

Regular fluid and filter changes are the most effective way to prevent these common problems and ensure your 2019 Silverado 2500HD provides many years of reliable service.

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