Chevrolet Silverado / GMC Sierra. Service manual — part 746

Fig. 19: Identifying Black Supply Hose & Clear Waste Hose
Courtesy of GENERAL MOTORS CORP.

1. Disconnect the supply and waste hoses from the vehicle cooler lines. Reverse the supply and

waste hoses to provide a normal flow direction.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Fig. 20: Setting Main Function Switch To FLUSH Position
Courtesy of GENERAL MOTORS CORP.

2. Turn the main function switch to the FLUSH position and allow machine to operate for 30

seconds.

FLOW TEST

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Fig. 21: Setting Main Function Switch To FLOW Position
Courtesy of GENERAL MOTORS CORP.

1. Turn the main function switch to the FLOW position and allow the oil to flow for 15

seconds. Observe and note the flow rate; this is the TESTED flow rate.

2. Compare the TESTED flow rate to the MINIMUM flow rate information previously

recorded.

If the TESTED flow rate is equal to or greater than the MINIMUM flow rate
recorded, the oil cooling system is functioning properly. Perform Code Recording

IMPORTANT: If the flow rate is less than 0.5 gpm, the LCD displays an

error message. Refer to the Troubleshooting section of the
tester operation manual.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Procedure.

If the TESTED flow rate is less than the MINIMUM flow rate previously recorded,
repeat the back flush and forward flush procedures.

3. If the TESTED flow rate is less than the MINIMUM flow rate after the second test, perform

Code Recording Procedure.

1. Replace the transmission oil cooler.

2. Reconnect supply and waste hoses to the cooler lines in the normal flow direction.

Perform Flow Test.

3. Perform Code Recording Procedure.

CODE RECORDING PROCEDURE

Fig. 22: Setting Main Function Switch To CODE Position
Courtesy of GENERAL MOTORS CORP.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado