Chevrolet Trax: Road test

NOTE: The Road Test Procedure should be performed only as part of the Symptom Diagnosis.

Perform the road test in conjunction with 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 and Torque Converter Clutch (TCC) Apply
• Part Throttle Step-In 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 Level and Condition 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.
• Ensure the transmission fluid temperature is at least 90ºC (194ºF).

After the road test, check the following:

• Inspect for proper transmission fluid level. Refer to Transmission Fluid Level and Condition 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 (Non Hybrid).

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. Verify that the following scan tool data can be obtained and is functioning properly.

Refer to Control Module References for typical data values. Data that is questionable may indicate a concern.

• Engine Speed
• Transmission ISS
• Transmission OSS
• Vehicle Speed
• IMS
• Commanded Gear
• Gear Ratio
• Line PC Sol. Pressure Cmd.
• Brake Switch
• ECT, Engine Data List
• Trans. Fluid Temp.
• TCM Temperature
• Calc. Throttle Position
• Ignition Voltage
• 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
• Shift Solenoid 2
• TCC PC Sol. Duty Cycle
• TCC Slip Speed

5. Check the garage shifts.

1. Apply the brake pedal and ensure the parking brake is set.
2. Move the gear selector through the following ranges:

1. PARK to REVERSE
2. REVERSE to NEUTRAL
3. NEUTRAL to DRIVE
4. DRIVE to REVERSE
5. REVERSE to DRIVE

3. Pause 2 to 3 seconds in each gear position.
4. Verify the gear engagements are immediate (less than 2 seconds to complete if transmission fluid temperature is above 20ºC (68ºC) and not harsh. Note that these shifts may be almost imperceptible in some applications. Using the scan tool to monitor Transmission ISS achieving 0 rpm can be used to check delay in these cases.

NOTE:

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

• High engine idle speed-Compare engine idle speed to desired idle speed.
• Incorrect line pressure-Investigate Line PC Sol. Pressure Cmd. kPa (psi), also perform Line Pressure Check.
• A default condition caused by certain DTCs that result in maximum line pressure to prevent clutch slippage.
• Incomplete adapting or incorrect adapting-Repeat maneuver multiple times to see if shift quality improves. If it does not, refer to the service procedures for Harsh Garage Shift.

NOTE:

Delayed engagement may be caused by any of the following conditions:

• Low idle speed-Compare engine idle speed to desired idle speed.
• Low fluid level
• Incorrect line pressure-Investigate Line PC Sol. Pressure Cmd. kPa (psi), also perform Line Pressure Check.
• Cold transmission fluid temperature (TFT)-Use the scan tool to determine TFT.
• Selector linkage-Inspect and adjust as necessary.
• Incomplete adapting or incorrect adapting-Repeat maneuver multiple times to see if delay improves. If it does not, refer to the service procedures for Harsh First and Reverse Shift.

6. Monitor transmission range on the scan tool, transmission data list.

1. Apply the brake pedal and ensure the parking brake is set.
2. Move the gear selector through all ranges.
3. Pause 2 to 3 seconds in each range.
4. Return gear selector to PARK.
5. Verify that all selector positions match the scan tool display.

7. Check throttle position input.

1. Apply the brake pedal and ensure the parking brake is set.
2. Ensure the gear selector is in PARK.
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 and Torque Converter Clutch (TCC) Apply

The TCM calculates the upshift points based primarily on 2 inputs: throttle position and vehicle speed. When the TCM determines that conditions are met for a shift to occur, the TCM commands the shift by varying current to the appropriate PC solenoids to control oncoming and offgoing clutch pressures.

Perform the following steps:

1. Monitor the following scan tool parameters:

• Calc. Throttle Position
• Vehicle Speed
• Engine Speed
• Transmission ISS
• Transmission OSS
• Commanded Gear
• TCC PC Sol. Pressure Cmd.
• TCC Slip Speed
• 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

2. Place the gear selector in the DRIVE position.
3. Accelerate the vehicle using a steady throttle position between 15 and 20 percent. Hold the throttle steady.
4. 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 PC solenoid pressure command should chang to "YES" for the oncoming clutch and the PC solenoid pressure command should change to "NO" for the offgoing clutch.
5. Note any harsh, soft or delayed shifts or slipping. Note any noise or vibration.
6. The TCC feel may not be noticeable. In many applications the TCC will apply after the 1-2 shift and TCC events will not be easily detected using engine speed.

NOTE: This transmission is equipped with an electronically controlled capacity clutch (ECCC), which allows operation of the clutch without fully locking to the torque converter cover. The clutch maintains a small amount of slippage, approximately 20 RPM, in 2nd, 3rd, 4th, 5th, and 6th gears, depending on the vehicle application. ECCC was developed to reduce the possibility of noise, vibration or chuggle caused by TCC apply. Full lockup is available at highway speeds on some applications.

7. Monitor TCC PC solenoid pressure command while driving and check TCC slip speed when the pressure command indicates that the TCC is commanded to apply:

When the TCC applies, slip speed should be controlled to below 100 RPM when the transmission is not shifting and the throttle is held steady. If the TCC slip exceeds this value for more than 6 seconds after the TCC PC Sol. Pressure Command indicates that the TCC is commanded on:

• Check for DTCs.
• Refer to Torque Converter Diagnosis.

Part Throttle Step-In Downshifts

1. Place the gear selector in the DRIVE position.
2. Accelerate the vehicle at light throttle (5-15 percent) until 3rd gear is just achieved.
3. Quickly increase throttle angle until commanded gear indicates that a downshift to 2nd gear is commanded.
4. Verify that the transmission downshifts within 2 seconds of the throttle movement.
5. Repeat steps 2 to 4 at higher speed to achieve 4th gear and then step in to command a 4th gear to 3rd gear downshift.
6. Repeat steps 2 to 4 at higher speed to achieve 5th gear and then step in to command a 5th to 4th gear downshift.
7. Repeat steps 2 to 4 at higher speed to achieve 6th gear and then step in to command a 6th gear to 5th gear downshift.
8. Note any harsh, soft or delayed shifts or slipping. Note any noise or vibration.

Manual Downshifts

Manual downshift testing is not required since all vehicles equipped are also equipped with some form of Driver Shift Control(DSC). The TCM 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 6th gear with the TCC applied.
3. Release the throttle and apply the brakes
4. Verify that the downshifts occur as commanded by monitoring gear ratio, which should change after commanded gear changes.

Manual Gear Range Selection

This application does not utilize manual forward gear ranges.

Reverse

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 the type of DSC available in this application. Utilize the DSC to ensure that the transmission responds appropriately to driver's commands. The TCM will upshift automatically when maximum engine speed is achieved and will protect from any downshift which may cause excessive engine RPMs.

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