Chevrolet Silverado / GMC Sierra. Manual — part 827

2008 TRANSMISSION

Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

SYMPTOMS - AUTOMATIC TRANSMISSION

The following table consists of six diagnostic categories that are located in the left-hand column.
Using this column, choose the appropriate category based on the operating conditions of the
vehicle or transmission. After selecting a category, use the right-hand column to locate the
specific symptom diagnostic information.

Diagnostic Category

Diagnostic Information

IMPORTANT:

The Functional Test Procedure should be performed before beginning any diagnosis. If this
procedure has not already been performed, refer to Functional Test.

Fluid Diagnosis:
This category contains the following topics:

Fluid condition - appearance,
contaminants, smell, overheating

Line pressure - high or low

Low lubrication pressure

Fluid leaks

Refer to Transmission Fluid Check.

Refer to Transmission Overheats.

Refer to Low Main Line Pressure in
All Ranges.

Refer to Low Main Line Pressure in
Specific Ranges, Normal Pressure in
Other Ranges.

Refer to Low Lubrication Pressure.

Refer to Fluid Leak Diagnosis.

Refer to Fluid Leaks from Fluid Fill
Tube and/or Vent.

Refer to Fluid Leaks from
Transmission Input.

Refer to Fluid Leaks from
Transmission Output.

Refer to Contaminated Transmission
Fluid.

Refer to Intermittent Buzzing Noise.

Noise and Vibration Diagnosis:
This category contains the following topics:

Refer to Noise and Vibration
Analysis.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

FUNCTIONAL TEST

Noise - drive gear, final drive, whine,
growl, rattle, buzz, popping

Vibration

Refer to Flexplate/Torque Converter
Vibration Test.

Range Performance Diagnosis:
This category contains the following topics:

Drives in Neutral

Excessive creep

Will not shift to Forward or Reverse

Will not stay in Forward or Reverse

Will not make a specific shift

Refer to Abnormal Activities or
Responses.

Refer to Transmission Will Not Shift
to Forward or Reverse.

Refer to Transmission Will Not Stay
in Forward or Reverse.

Refer to Transmission Will Not Make
a Specific Shift.

Shift Quality - Feel Diagnosis:
This category contains the following topics:

Erratic shifts

Harsh, soft, delayed or slipping shifts

Harsh, soft, or delayed engagement

Refer to Transmission Does Not Shift
Properly.

Refer to Excessive Slippage and
Clutch Chatter.

Refer to Excessive Flare - Engine
Overspeed on Wide-Open Throttle.

Shift Speed Diagnosis:
This category contains the following topic:
Inaccurate or inconsistent shift points

Refer to Transmission Does Not Shift
Properly.

Torque Converter Diagnosis:
This category contains the following topics:

Poor performance

Noise during converter operation

TCC shudder

Shudder after TCC apply

Vibration during converter operation

Refer to Torque Converter Diagnosis.

Refer to Flexplate/Torque Converter
Vibration Test.

Step

Action

Yes

No

The Functional Test Procedure is the first step in diagnosing mechanical or hydraulic
transmission conditions. The Functional Test Procedure provides procedures and references
to the symptom diagnosis table for specific diagnostic information.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

1

Verify the customer concern.Has the customer
concern been verified?

IMPORTANT:

Engine performance can strongly affect
transmission performance. Ensure the condition
is not the result of poor engine performance
before continuing.

Go to Step 2

-

2

Perform the Diagnostic System Check -
Vehicle .Did you perform the Diagnostic
System Check - Vehicle?

IMPORTANT:

Many transmissions have default actions that
take place once a DTC fault is detected. These
actions may appear to be transmission concerns.

Go to Step 3

Go to Diagnostic

System Check -

Vehicle

3

Inspect for the following conditions:

Vehicle damage

Transmission oil pan damage

Refer to Oil Pan Replacement.

Transmission range selector cable
damaged or out of adjustment

Refer to Range Selector Lever Cable
Adjustment or Range Selector Lever
Cable Replacement.

Inspect for the following loose, worn,
damaged, or missing components:

Mounts or struts

Brackets

Mounting hardware

Refer to Transmission
Replacement .

Transmission cooler or cooler line

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

restrictions

Refer to Transmission Fluid Cooler
Flushing and Flow Test.

Fluid leaks

Refer to Fluid Leak Diagnosis.

Did you find a condition?

Go to the

appropriate repair

or diagnosis

section

Go to Step 4

4

Perform the Transmission Fluid Check.
Did you perform the Transmission Fluid
Check ?

Go to Step 5

Go to

Transmission

Fluid Check

5

Perform the Road Test.
Did the vehicle exhibit any objectionable
performance condition?

Go to Step 6

Go to Step 1

6

Did the vehicle exhibit objectionable torque
converter operation?

Go to Step 15

Go to Step 7

7

Did the vehicle produce any objectionable
noise condition?

Go to Symptoms

- Automatic

Transmission

Go to Step 8

8

Did the vehicle exhibit a vibration condition?

Go to Step 9

Go to Step 10

9

Did the vibration occur only during torque
converter clutch (TCC) apply or release?

Go to Step 15

Go to Symptoms

- Automatic

Transmission

10

Did the vehicle exhibit a shift speed
condition, such as low or high shift speeds?

Go to Symptoms

- Automatic

Transmission

Go to Step 11

11

Inspect for the following unacceptable shift
qualities:

Harsh, soft, delayed, or no engagement

Harsh, soft, or delayed shifts

Shift shudder, flare, or tie-up

Did the vehicle exhibit any of these shift
quality conditions?

Go to Step 12

Go to Step 13

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado