GM Service Manual Online
For 1990-2009 cars only

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Action

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

1

Important: Engine performance can greatly affect transmission performance. Ensure that the condition is not the result of poor engine performance before continuing.

Verify the customer concern.

Has the customer concern been verified?

Go to Step 2

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2

Important: Many transmissions have default actions that take place once a DTC fault is detected. These actions may be interpreted as being a transmission condition.

Did you perform the Diagnostic System Check - Automatic Transmission ?

Go to Step 3

Go to Diagnostic System Check - Automatic Transmission

3

Perform a visual inspection.

Inspect for the following conditions:

    • Vehicle damage
    • Transmission oil pan damage.
        Refer to Oil Pan Replacement .
    • Worn or damaged suspension parts.
        Refer to Diagnostic Starting Point - Suspension General Diagnosis in Suspension General Diagnosis.
        Worn or damaged steering parts
        Refer to Symptoms - Power Steering System in Power Steering System.
    • Transmission range selector cable damaged or out of adjustment
        Refer to Shift Cable Adjustment or Shift Cable Replacement .
    • Loose, worn, damaged or missing:
       - mounts or struts
       - brackets
       - mounting hardware
       - Refer to Transmission Replacement .
    • Transmission cooler or cooler line restrictions
    • Fluid leaks
        Refer to Fluid Leak Diagnosis .

Did you identify an item that needs service?

Go to the appropriate Repair or Diagnosis section

Go to Step 4

4

Perform the Transmission Fluid Check .

Did you perform the Transmission Fluid Checking Procedure?

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 Noise and Vibration Diagnosis

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 Noise and Vibration Diagnosis

10

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

Go to Symptoms - Automatic Transmission Shift Speed Diagnosis

Go to Step 11

11

Did the vehicle exhibit any of the following shift quality, feel, conditions?

    • Harsh, soft, delayed or no engagement
    • Harsh, soft or delayed shifts
    • Shift shudder, flare or tie-up

Go to Step 12

Go to Step 13

12

Perform the Line Pressure Check .

Is the line pressure within specification?

Go to Symptoms - Automatic Transmission Shift Quality - Feel Diagnosis

Go to Symptoms - Automatic Transmission Fluid Diagnosis

13

Did the vehicle exhibit any of the following shift pattern conditions?

    • No upshift or downshift
    • Only one or two forward ranges
    • No FIRST range, SECOND range, THIRD range, FOURTH range or FIFTH range
    • Slipping
    • Non FIRST range start

Go to Symptoms - Automatic Transmission Shift Pattern Diagnosis

Go to Step 14

14

Did the vehicle exhibit any of the following range performance conditions?

    • No PARK, REVERSE or DRIVE
    • No engine braking
    • No gear selection
    • Incorrect gear selection

Go to Symptoms - Automatic Transmission Range Performance Diagnosis

System OK

15

Did the vehicle exhibit any of the following torque converter or TCC conditions?

    • Stuck ON or OFF
    • Early or late engagement
    • Incorrect apply or release
    • Soft or harsh apply
    • Clunk or shudder
    • No torque multiplication
    • Excessive slip
    • Poor acceleration
    • Engine stalls

Refer to Torque Converter Diagnosis .

Go to Symptoms - Automatic Transmission Torque Converter Diagnosis

System OK