GM Service Manual Online
For 1990-2009 cars only

Functional Test Procedure (1999 4L80-E C/K Truck)

Step

Action

Value(s)

Yes

No

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 complaint is not the result of poor engine performance before continuing.

Verify the customer complaint.

Has the customer complaint been verified?

--

Go to Step 2

--

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 concern.

Has the Powertrain On Board Diagnostic (OBD) System Check 5.7L or Powertrain On Board Diagnostic (OBD) System Check 6.5L or Powertrain On Board Diagnostic (OBD) System Check 7.4L been performed?

--

Go to Step 3

Go to Powertrain On Board Diagnostic (OBD) System Check 5.7L

Go to Powertrain On Board Diagnostic (OBD) System Check 6.5L

Go to Powertrain On Board Diagnostic (OBD) System Check 7.4L

3

Perform a visual inspection. Look for the following conditions:

    • Vehicle damage
    • Transmission oil pan damage. Refer to AT Fluid/Filter Changing.
    • Worn or damaged suspension parts. Refer to Front Suspension.
        Worn or damaged steering parts. Refer to Steering.
    • Transmission range selector cable damaged or out of adjustment.
        Refer to Shift Cable Replacement or Shift Cable Adjustment .
    • 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 .

Was an item identified that needs service?

--

Go to the Appropriate Repair or Diagnosis Section

Go to Step 4

4

Perform the Transmission Fluid Check .

Is the procedure complete?

--

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 Symptom Diagnosis (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 TCC apply or release?

--

Go to Step 15

Go to Symptom Diagnosis (Noise and Vibration Diagnosis)

10

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

--

Go to Symptom Diagnosis (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 Symptom Diagnosis (Shift Quality (Feel) Diagnosis)

Go to Symptom Diagnosis (Fluid Diagnosis)

13

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

    • No upshift or downshift
    • Only one or two forward gears
    • No FIRST gear, no SECOND gear, No THIRD gear, or no FOURTH gear
    • Slipping
    • Non-FIRST gear start

--

Go to Symptom Diagnosis (Shift Pattern Diagnosis)

Go to Step 14

14

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

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

--

Go to Symptom Diagnosis (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 Symptom Diagnosis (Torque Converter Diagnosis Procedure)

System OK