GM Service Manual Online
For 1990-2009 cars only

Note: The Road Test Procedure should be performed only as part of the Symptom Diagnosis. Refer to Symptoms - Automatic Transmission.

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
    • Part Throttle Detent Downshifts
    • Manual Downshifts
    • Coasting Downshifts
    • Manual Gear Range Selection
       - REVERSE
       - Driver Shift Control

Note: Complete the test in the sequence given. Incomplete testing cannot guarantee an accurate evaluation.

Before the road test, ensure the following:

    • The engine is performing properly.
    • Transmission fluid level is correct. Refer to Transmission Fluid Check.
    • Tire pressure is correct.

During the road test:

    • Perform the test only when traffic conditions permit.
    • Operate the vehicle in a controlled, safe manner.
    • Observe all traffic regulations.
    • View the scan tool data while conducting this test.
        Take along qualified help in order to operate the vehicle safely.
    • Observe any unusual sounds or smells.

After the road test, check the following:

    • Inspect for proper transmission fluid level. Refer to Transmission Fluid Check.
    • Inspect for any diagnostic trouble codes (DTCs) that may have set during the testing. Refer to the applicable DTC.
    • Monitor the scan tool data for any abnormal readings or data.
    • Inspect for fluid leaks. Refer to Fluid Leak Diagnosis.

Electrical Function Check

Perform this procedure first in order to ensure the electronic transmission components are functioning properly. If these components are not checked, a simple electrical condition could be misdiagnosed.

  1. Connect the scan tool.
  2. Ensure the gear selector is in PARK and set the parking brake.
  3. Start the engine.
  4. Note: Note that the engine may go in to AutoStop Mode depending on which gear is selected and many other variables. For more information on AutoStop Mode refer to Hybrid Modes of Operation Description.

  5. Verify that the following scan tool data can be obtained and is functioning properly.
  6. Refer to Control Module References for typical data values. Data that is questionable may indicate a concern.

    • Engine Torque
    • Drvr Axle Torque Request
    • APP Indicated Angle
    • Engine Speed
    • Calc. Trans Input Speed
    • Transmission OSS
    • OSS Supply Voltage
    • Vehicle Speed
    • Output Shaft Direction
    • Clutch 1 Slip Speed
    • Clutch 2 Slip Speed
    • Clutch 3 Slip Speed
    • Clutch 4 Slip Speed
    • Clutch 1 Status
    • Clutch 2 Status
    • Clutch 3 Status
    • Clutch 4 Status
    • IAT
    • BPP Signal
    • Shift Solenoid 1
    • Shift Solenoid 2
    • Gear Ratio
    • Driver Shift Control
    • Driver Shift Request
    • IMS A/B/C/P
    • IMS
    • TFP Switch 1
    • TFP Switch 3
    • TFP Switch 4
    • TFP Switch 5
    • ECT
    • Trans. Fluid Temp.
    • TCM Temperature
    • PC Sol. 2 Pressure Cmd.
    • PC Sol. 3 Pressure Cmd.
    • PC Sol. 4 Pressure Cmd.
    • PC Sol. 5 Pressure Cmd.
    • Line PC Sol. Pressure Cmd.
    • Engine Run Time
    • EC Ignition Relay Feedback Signal
    • Ignition Voltage
  7. Check the garage shifts.
  8. 5.1. Apply the brake pedal and ensure the parking brake is set.

            Note: If the vehicle was in the AutoStop Mode the engine will start and run when the gear selector is placed in Reverse and M (Manual). If the gear selector is moved very quickly through these ranges and is in the AutoStop Mode the engine will not restart.

    5.2. Move the gear selector through the following ranges:
             5.2.1. PARK to REVERSE
             5.2.2. REVERSE to NEUTRAL
             5.2.3. NEUTRAL to DRIVE
    5.3. Pause 2 to 3 seconds in each gear position.
    5.4. Verify the gear engagements are immediate and not harsh.

            Note: These shifts can not be felt when trans is functioning properly.

    Note: Harsh engagement may be caused by any of the following conditions:

       • High engine idle speed--Compare engine idle speed to desired idle speed.
       • Commanded low pressure control (PC) solenoid current--Investigate PC Sol. Pressure Cmd. kPa (psi) for all solenoids. High pressure will cause harsh shifts.
       • A default condition caused by certain DTCs that result in maximum line pressure to prevent clutch slippage.

    Note: Soft or delayed engagement may be caused by any of the following conditions:

       • Low idle speed--Compare engine idle speed to desired idle speed
       • Low auxiliary pump pressure in autostop only
       • Low fluid level
       • Commanded high PC solenoid current--Investigate PC Sol. Pressure Cmd. kPa (psi) for all solenoids. Low pressure will cause soft or delayed shifts
       • Cold transmission fluid temperature (TFT)--Use the scan tool to determine TFT
       • Selector linkage--Inspect and adjust as necessary

  9. Monitor transmission range on the scan tool, trans data list.
  10. 6.1. Apply the brake pedal and ensure the parking brake is set.
    6.2. Move the gear selector through all ranges.
    6.3. Pause 2 to 3 seconds in each range.
    6.4. Return gear selector to PARK.
    6.5. Verify that all selector positions match the scan tool display.
  11. Check throttle position input.
  12. 7.1. Apply the brake pedal and ensure the parking brake is set.
    7.2. Ensure the gear selector is in PARK.
    7.3. Monitor the scan tool Calc. Throttle Position while increasing and decreasing engine speed with the throttle pedal. The scan tool Calc. Throttle Position percentage should increase and decrease with engine speed.

If any of the above checks do not perform properly, record the result for reference after completion of the road test.

Upshift Control

The hybrid powertrain control module (HPCM) calculates the upshift points based primarily on 2 inputs: throttle position and vehicle speed. When the HPCM determines that conditions are met for a shift to occur, the HPCM commands the shift by closing or opening the ground circuit for the appropriate solenoid.

Perform the following steps:

  1. Choose a throttle position of 12 percent or 25 percent. All throttle positions shown should be tested to cover the normal driving range.
  2. Monitor the following scan tool parameters:
  3. • Calc. Throttle Position
    • Vehicle Speed
    • Engine Speed
    • Transmission OSS
    • Commanded Gear
    • TFP Switch 1
    • TFP Switch 3
    • TFP Switch 4
    • TFP Switch 5
    • PC Sol. 2 Pressure Cmd.
    • PC Sol. 3 Pressure Cmd.
    • PC Sol. 4 Pressure Cmd.
    • PC Sol. 5 Pressure Cmd.
    • Shift Solenoid 1 and 2
  4. Place the gear selector in the DRIVE position.
  5. Accelerate the vehicle using the chosen throttle position. Hold the throttle steady.
  6. As the transmission upshifts, there should be a noticeable shift feel or engine speed change within 1 to 2 seconds of the commanded gear change. The feel may not be noticeable. Look for 100-300 RPM engine speed change.
  7. Shift speeds may vary slightly due to TFT or other operating variables, including hydraulic delays in responding to electronic controls.
  8. • Note any harsh, soft or delayed shifts or slipping.
    • Note any noise or vibration.

Part Throttle Downshift

  1. Place the gear selector in the DRIVE position.
  2. Accelerate the vehicle to 64-88 km/h (40-55 mph) in 4th gear.
  3. Quickly increase throttle angle to between 25-30 percent.
  4. Verify the transmission downshifts immediately.

Manual Downshifts

Manual downshift testing is not required for vehicles equipped with Driver Shift Control (DSC). This is done by shifting the gear selector to M on the display and then by using the + and - on the rocker switch on the gear selector. The TCM and shift solenoids will automatically override DSC downshifts to protect the transmission from damage.

Coasting Downshifts

  1. Place the gear selector in the DRIVE position.
  2. Accelerate the vehicle to 4th gear.
  3. Release the throttle and apply the brakes
  4. Verify the downshifts occur as commanded.

Accelerating Upshifts

  1. Place the gear selector in the M position.
  2. Press the - until the display shows M1.
  3. Accelerate slowly and keep the throttle steady not going over 3,000 RPM Engine speed.
  4. Press the + on the gear selector.
  5. Verify the upshift occurs as commanded. Repeat step 4 to verify the remaining gears.

Manual Gear Range Selection

Reverse

Note: When the gear selector is placed in Reverse and the vehicle is in AutoStop Mode the Engine will start.

Perform the following test using a 10-15 percent throttle position.

  1. With the vehicle stopped, move the gear selector to REVERSE.
  2. Slowly accelerate the vehicle.
  3. Verify that there is no noticeable slip, noise or vibration.

Driver Shift Control (DSC)

Refer to the owner's manual for specific instructions on DSC. The TCM will upshift automatically when maximum engine speed is achieved and will protect from any downshift which may cause excessive engine RPMs.