GM Service Manual Online
For 1990-2009 cars only

Perform this test using a scan tool.

Perform this test only when traffic and road conditions permit.

Observe all traffic safety regulations.

Garage Shifts

Perform the garage shift test prior to continuing the road test to make sure the PCM/TCM inputs are connected and functioning properly.

  1. Move the transaxle control assembly to Park (P) and set the parking brake.
  2. Connect a scan tool to the DLC.
  3. Start the engine.
  4. Verify the following signals are present on the scan tool:
  5. • Engine Speed (RPM)
    • Transmission ISS
    • Transmission OSS
    • Vehicle Speed
    • TR Switch - P/A/B/C
    • TFP Range
    • PC Solenoid Ref. Current
    • PC Solenoid Actual Current
    • PC Solenoid Duty Cycle
    • Brake Switch
    • Engine Coolant Temperature (ECT)
    • Trans. Fluid Temp.
    • TP Angle
    • Ignition 1
    • Transmission Range
  6. Monitor the BRAKE SWITCH signal while tapping on the brake pedal with your foot. The brake switch signal should be:
  7. Released -- When the brake pedal is released.

    Applied -- When the brake pedal is applied.

  8. Monitor the TRANSMISSION RANGE signal and move the gear selector through all ranges. Verify the TRANSMISSION RANGE value matches the gear range selected on the console. The gear selections should be immediate and not harsh.
  9. Move the control assembly to Neutral (N) and monitor the throttle angle signal while increasing and decreasing the engine RPM with the accelerator pedal. The throttle angle should increase with engine RPM.
  10. Check for and note any diagnostic trouble codes (DTCs).

Upshift Control and Torque Converter Clutch (TCC) Apply

With the gear selector in Overdrive (D), perform the following steps:

  1. Refer to the Shift Speed table contained in the Specifications section of this service manual and choose a throttle position of either 10 percent or 25 percent.
  2. Monitor the TP angle and vehicle speed with the scan tool.
  3. Important: Shift speeds may vary due to slight hydraulic delays in responding to electronic controls. A change from the original equipment tire size also affects shift speeds.

  4. Accelerate to the chosen TP angle. Hold the throttle steady.
  5. As the transaxle upshifts, note the shift speed and commanded gear changes for each of the following gears:
  6. • 2nd gear
    • 3rd gear
    • 4th gear

    Important: The torque converter clutch (TCC) should not apply unless the transaxle has reached a minimum operating temperature of 8°C (46°F) trans temp and 50°C (122°F) engine coolant temp.

  7. The torque converter clutch (TCC) should apply in Fourth gear. Note when the TCC applies. An RPM drop will occur when the TCC applies.
  8. Repeat steps 1-5 using several different throttle angles.

Part Throttle Detent Downshift

At vehicle speeds of 64-88 km/h (40-55 mph) in Fourth gear, quickly increase the TP angle to greater than 50 percent. Verify the following results:

    • The TCC releases.
    • The transaxle downshifts to 3rd gear.
    • The 1-2 shift solenoid turns OFF.
    • The 2-3 shift solenoid remains ON.

Full Throttle Detent Downshift

At vehicle speeds of 64-88 km/h (40-55 mph) in Fourth gear, quickly increase the TP angle to its maximum position. Verify the following results:

    • The TCC releases.
    • The transaxle downshifts to 2nd gear immediately.
    • The 1-2 and 2-3 shift solenoid turns OFF.

Manual Downshifts

The shift solenoids do not control the initial 4-3 manual downshift. The 4-3 manual downshift is hydraulic. The 3-2 and 2-1 manual downshifts are electronic. The solenoid states will change during, or shortly after, a 4-3 downshift is selected.

  1. At vehicle speeds of 64-88 km/h (40-55 mph) in Fourth gear, release the accelerator pedal while moving the gear selector to manual Third (3). Observe the following results:
  2. • The TCC releases.
    • The transaxle downshifts to 3rd gear immediately.
    • The engine slows the vehicle down.
  3. Move the gear selector back to Overdrive (D) and accelerate to 64-72 km/h (40-45 mph). Release the accelerator while moving the gear selector to manual Second (2) and observe the following results:
  4. • The TCC releases.
    • The transaxle immediately downshifts to 2nd gear.
    • The engine slows the vehicle down.
  5. Move the gear selector back to Overdrive (D) and accelerate to 64 km/h (40 mph). Release the accelerator pedal while moving the gear selector to manual First (1) and observe the following results:
  6. • The TCC releases.
    • The transaxle immediately downshifts to 2nd gear.
    • The engine slows the vehicle down.
    • Below 60 km/h (37 mph), the transaxle downshifts to 1st gear.

A Manual First-Third Gear Ratio will occur at high speeds as an upshift safety feature. Do not attempt to perform this shift.

Manual Gear Range Selection

The shift solenoid controls upshifts in manual gear ranges. Perform the following tests by accelerating at 10 percent TP sensor position.

Manual Third (3)

With the vehicle stopped, move the gear selector to manual Third (3) and accelerate in order to observe the following conditions:

    • The 1-2 shift
    • The 2-3 shift

Manual Second (2)

  1. With the vehicle stopped, move the gear selector to manual Second (2) and accelerate in order to observe the 1-2 shift.
  2. Accelerate to 40 km/h (25 mph) and observe the following conditions:
  3. • The 2-3 shift does not occur.
    • The TCC does not apply.

Manual First (1)

With vehicle stopped, move gear selector to Manual First (1). Accelerate to 32 km/h (20 mph) and observe the following conditions:

    • No upshifts occur.
    • The TCC does not apply.

Reverse (R)

With vehicle stopped, move gear selector to R and slowly accelerate in order to observe the following conditions:

    • The 1-2 Shift Solenoid is ON.
    • The 2-3 Shift Solenoid is OFF.

Use a scan tool to see if any engine/transaxle trouble codes are set. Refer to Diagnostic Trouble Codes and repair the vehicle as directed. After repairing the vehicle, verify the code did not set again.

If the transaxle is still not performing well but no trouble codes have set, there may be an intermittent condition. Check all electrical connections for damage or a loose fit. Some scan tools have a snapshot test which can help catch an intermittent condition that does not occur long enough to set a code.

If no DTCs are set and the condition is suspected to be hydraulic, take the vehicle on a road test.