Complete transmission fluid exchange procedure for the 8L90 8-speed automatic transmission, including pan removal, filter replacement, and fluid refill to restore optimal transmission performance.

Warnings

Tools required

Parts

• Transmission fluid filter kit × 1 — ACDelco 24273598 or equivalent
• Transmission pan gasket × 1 — ACDelco 24284583 or equivalent
• Transmission pan magnet (if not included with filter kit) × 1 — Use OEM specification

Fluids

• ACDelco Dexron VI ATF — 11.5 qt

Preparation

1. Park vehicle on level surface and engage parking brake. Place wheel chocks behind rear wheels.
2. Start engine and allow transmission to reach normal operating temperature, then shut off and allow to cool for 2 hours minimum.
3. Raise front of vehicle with floor jack and support securely on jack stands at manufacturer-specified lift points on frame rails.
4. Remove skid plate or belly pan if equipped (varies by trim level).
5. Locate transmission pan at rear of engine bay, beneath transmission housing.

Procedure

1. 1

   Drain transmission fluid from pan
   Position drain pan underneath transmission pan. Starting at one rear corner, carefully loosen transmission pan bolts in a criss-cross pattern, leaving 2-3 bolts partially threaded at opposite corners. Gently pry the loosened edge down to allow fluid to drain in a controlled manner. Once fluid flow slows, remove remaining bolts and lower pan completely. Be prepared for approximately 5-6 quarts of fluid to drain.
   ⚠Fluid will drain quickly once pan is loosened. Keep hands and face clear of draining fluid.
2. 2

   Remove and inspect old filter
   Locate the transmission filter assembly attached to the valve body inside the transmission. The 8L90 uses a spin-on style filter. Rotate filter counterclockwise to remove. Inspect old filter for metal debris or excessive contamination. Check pan magnet for metal shavings (light metallic dust is normal; large chunks indicate internal wear).
   ℹ️Additional fluid (1-2 quarts) will drain when filter is removed. Keep drain pan positioned underneath.
3. 3

   Clean transmission pan and mating surface
   Remove all old gasket material from transmission pan using plastic scraper. Clean pan interior thoroughly with solvent and wipe dry. Clean magnet and reinstall in pan if removed. Use wire brush and gasket remover to clean transmission case mating surface, ensuring all old gasket material and RTV are completely removed. Wipe surface clean with shop towel.
   ⚠Do not allow debris or gasket material to fall into open transmission. Cover opening with clean shop towel during cleaning.
4. 4

   Install new transmission filter
   Lightly lubricate new filter O-ring with clean Dexron VI ATF. Install new filter by rotating clockwise until it seats firmly and O-ring contacts valve body. Hand tighten only; do not use tools to install filter as this may damage the seal.
5. 5

   Install new gasket and reinstall pan
   Position new gasket on transmission pan (or apply gasket to transmission case mating surface per gasket manufacturer instructions). Carefully lift pan into position, ensuring gasket remains aligned. Start all pan bolts by hand to prevent cross-threading. Tighten bolts in a criss-cross pattern from center outward, working in multiple passes to ensure even gasket compression.
   Torque spec

   Pan Bolts20 Nm (15 lb-ft)
6. 6

   Refill transmission with fresh fluid
   Locate transmission fill plug on passenger side of transmission case. Remove fill plug. Using fluid transfer pump or funnel with extension hose inserted into fill hole, add 6 quarts of ACDelco Dexron VI ATF initially. Reinstall fill plug finger-tight (do not torque yet).
7. 7

   Start engine and circulate fluid
   Start engine and allow to idle in Park. Depress brake pedal and slowly shift through all gear positions (P-R-N-D-M and back to P), pausing 3-5 seconds in each gear. This circulates fluid through transmission and torque converter. Return to Park and allow engine to idle for 2-3 minutes.
   ⚠Ensure vehicle is securely supported on jack stands and parking brake is engaged before shifting gears.
8. 8

   Check fluid level and add as needed
   With engine running and transmission in Park, remove fill plug. Fluid should drip slowly from fill hole when transmission fluid temperature reaches 85-95°F (use scan tool to monitor temp, or wait approximately 5 minutes at idle). Add fluid in 1-pint increments through fill hole until fluid begins to drip out. Allow excess to drain until dripping slows to a trickle.
   ℹ️Proper fluid level is critical. Fluid should drip from fill hole at specified temperature. If fluid pours out quickly, transmission is overfilled.
9. 9

   Install fill plug and finalize
   With fluid at correct level and still dripping slowly, install fill plug and tighten to specification. Shut off engine. Reinstall skid plate or belly pan if equipped. Lower vehicle from jack stands.
   Torque spec

   Fill Plug42 Nm (31 lb-ft)

Reassembly

1. Reinstall any removed skid plates or belly pans with original hardware.
2. Double-check that all transmission pan bolts and fill plug are torqued to specification.
3. Dispose of used transmission fluid at appropriate recycling facility.

Verification

• Start engine and verify no fluid leaks from transmission pan or fill plug while idling.
• Test drive vehicle through all gears, verifying smooth shifts with no slipping, flaring, or harsh engagement.
• After test drive (10-15 minutes), recheck fluid level at operating temperature (85-95°F) with engine running in Park. Fluid should drip slowly from fill hole when plug is removed.
• Inspect transmission pan area and fill plug for any signs of seepage after vehicle has sat overnight.
• Monitor transmission operation over next 100 miles for any abnormal shifting behavior or fluid leaks.

More procedures for this vehicle