Chevrolet Silverado / GMC Sierra. Service manual — part 736

HOT CHECK PROCEDURE

1. Locate the transmission dipstick at the rear of the engine compartment, on the passemger's

side of the vehicle.

2. Flip the handle up, and then pull out the dipstick and wipe it with a clean rag or paper

towel.

3. Install the dipstick by pushing it back in all the way, wait three seconds and then pull it back

out again.

4. Check both sides of the dipstick, and read the lower level. Repeat the check procedure to

verify the reading.

5. Inspect the color of the fluid on the dipstick. Refer to Fluid Condition Inspection below.

6. A safe operating fluid level is within the HOT crosshatch band on the dipstick. If the fluid

level is not within the HOT band, and the TFT is between 160°F and 200°F (71°C and 93°
C), add or drain fluid as necessary to bring the level into the HOT band. If the fluid level is
low, add only enough fluid to bring the level into the HOT band. It does not take much
fluid, generally less than one pint (0.5L). Do not overfill. Also, if the fluid level is low,
inspect the transmission for leaks. Refer to Fluid Leak Diagnosis.

7. If the fluid level is in the acceptable range, push the dipstick back in all the way, then flip

the handle down to lock the dipstick in place.

8. If applicable and if the vehicle is equipped, reset the transmission oil life monitor only if the

fluid was changed.

FLUID CONDITION INSPECTION

Inspect the fluid color. The fluid should be red or dark brown.

IMPORTANT: Us this procedure to check the transmission fluid level when

the TFT is between 160°F and 200°F (71°C and 93°C). The hot
check procedure is the most accurate method to check the
fluid level. The hot check should be performed at the first
opportunity in order to verify the cold check. The fluid level
rises as fluid temperature increases, so it is important to
ensure the transmission temperature is within range.

IMPORTANT: Always check the fluid level at least twice. Consistent

readings are important to maintaining proper fluid level. If
inconsistent readings are noted, inspect the transmission
vent assembly to ensure it is clean and unclogged.

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

If the fluid color is very dark or black and has a burnt odor, inspect the fluid and inside of
the bottom pan for excessive metal particles or other debris. A small amount of "friction"
material in the bottom pan is a "normal" condition. If large pieces and/or metal particles are
noted in the fluid or bottom pan, flush the oil cooler and cooler lines and overhaul the
transmission. If there are no signs of transmission internal damage noted, replace the fluid
filter assembly, repair the oil cooler, and flush the cooler lines.

Fluid that is cloudy or milky or appears to be contaminated with water indicates engine
coolant or water contamination. Refer to Engine Coolant/Water in Transmission.

LINE PRESSURE CHECK

Fig. 6: View Of Transmission & J 21867 Pressure Gage
Courtesy of GENERAL MOTORS CORP.

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

TOOLS REQUIRED

J 21867 Pressure Gage

CHECK

1. Install a scan tool.

2. Start the engine.

3. Inspect the transmission for the proper fluid level. Refer to Transmission Fluid Check.

4. Use the scan tool to inspect for any active or stored diagnostic trouble codes.

5. Inspect the manual linkage at the transmission for proper function.

6. Turn the engine OFF.

7. Remove the line pressure test hole plug.

8. Install the J 21867 .

9. Access the Scan Tool Transmission Output Controls for the Line PC Solenoid.

10. Start the engine.

11. Use the scan tool to increase and decrease the Line PC Solenoid in increments of

approximately 100 KPa (15 psi). The scan tool commands the increment values
automatically.

12. Allow the pressure to stabilize between increments.

CAUTION: Keep the brakes applied at all times in order to prevent

unexpected vehicle motion. Personal injury may result if
the vehicle moves unexpectedly.

IMPORTANT: You may need to remove or disconnect components in order

to gain access to the transmission line pressure test hole
plug.

IMPORTANT: In order to achieve accurate line pressure readings, the

following procedure must be performed at least three times
in order to gather uniform pressure readings.
The scan tool is only able to control the line PC solenoid in
PARK and NEUTRAL with engine speeds below 1500 RPM.
This protects the clutches from extreme high or low line
pressures.

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

13. Compare your pressure readings on the scan tool to those indicated on the J 21867 .

14. If the pressure readings vary greatly, refer to Fluid Pressure High or Low.

15. Turn the engine OFF.

16. Remove the J 21867 .

17. Install the line pressure test hole plug.

Tighten: Tighten the pressure plug to 11 N.m (97 lb in).

ROAD TEST

The following test provides a method of evaluating the condition of the automatic transmission.
The test is structured so that most driving conditions would be achieved. The test is divided into
the following parts:

Electrical Function Check

Upshift Control and Torque Converter Clutch (TCC) Apply

Part Throttle Detent Downshifts

Manual Downshifts

Coasting Downshifts

Manual Gear Range Selection

REVERSE

Driver Shift Control

Before the road test, ensure the following:

The engine is performing properly.

Transmission fluid level is correct. Refer to Transmission Fluid Check.

NOTE:

Refer to Fastener Notice .

IMPORTANT: The Road Test Procedure should be performed only as part of the

Symptom Diagnosis. Refer to Symptoms - Automatic
Transmission.

IMPORTANT: Complete the test in the sequence given. Incomplete testing

cannot guarantee an accurate evaluation.

2008 Chevrolet Silverado 1500

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

Sierra & Silverado