Manufacturer communication — 2006 GMC YUKON DENALI XL

• Applies to 2021 and earlier GM passenger cars and trucks equipped with an automatic transmission.

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  Models: 2021 and Prior GM Passenger Cars and Trucks (including Chevrolet Medium Duty LCF Equipped with Gas Engine and 6L90 Transmission) Equipped with Automatic Transmission

• Water or ethylene glycol in the ATF changes the friction of the clutches, frequently causing shudder during engagement or gear changes, especially during torque converter clutch engagement.

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  Water or ethylene glycol in ATF will also change the friction of the clutches, frequently resulting in shudder during engagement or gear changes, especially during torque converter clutch engagement.

Steps to confirm (in the document’s order)

1. Signs of water in the ATF: ATF blowing out of the transmission vent tube; ATF that looks cloudy or, with extreme contamination, like a strawberry milkshake.

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   • ATF blowing out of the transmission vent tube. • ATF may appear cloudy or, in cases of extreme contamination, have the appearance of a strawberry milkshake.

2. Further signs: visible water in the oil pan, or a milky white substance inside the pan area.

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   • Visible water in the oil pan. • A milky white substance inside the pan area.

3. Further signs: spacer plate gaskets that appear glued to the valve body face or case, or swollen or wrinkled where they are not compressed.

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   • Spacer plate gaskets that appear to be glued to the valve body face or case. • Spacer plate gaskets that appear to be swollen or wrinkled in areas where they are not compressed.

4. Further sign: rust on internal iron/steel transmission components.

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   • Rust on internal transmission iron/steel components.

5. Test the ATF with the Gly-Tek test kit from the Nelco Company to decide accurately whether the radiator needs replacement.

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   The “Gly-Tek” test kit, available from the Nelco Company, should be obtained and the ATF tested to make an accurate decision on the need for radiator replacement.

6. Use the kit when water is found in the ATF and its source is not identified, or when a leaking in-radiator transmission oil cooler is suspected with no cross-contamination in the coolant recovery reservoir; it detects ethylene glycol in ATF.

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   If water in the ATF has been found and the source of the water entry has not been identified, or if a leaking in-radiator transmission oil cooler is suspected (with no evidence of cross-contamination in the coolant recovery reservoir), a simple and quick test kit is available that detects the presence of ethylene glycol in ATF.

Repair

1. If water or coolant is found in the transmission, replace all rubber-type seals, all composition-faced clutch plates and/or bands, and all nylon parts.

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   • Replace all of the rubber-type seals. • Replace all of the composition-faced clutch plates and/or bands. • Replace all of the nylon parts.

2. Also replace the torque converter, and thoroughly clean and rebuild the transmission using new gaskets and oil filter.

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   • Replace the torque converter. • Thoroughly clean and rebuild the transmission, using new gaskets and oil filter.

3. When repairing or replacing, flush and flow check the transmission oil cooler using J-45096.

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   • Flush and flow check the transmission oil cooler using J–45096.

4. Thoroughly inspect the engine cooling system and hoses, and clean/repair as necessary.

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   • Thoroughly inspect the engine cooling system and hoses and clean/repair as necessary.