Important: The Road Test Procedure should be performed only as part of the Functional
Test Procedure. Refer to
Functional Test
.
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 Detent Downshifts |
• | Full Throttle Detent Downshifts |
• | Manual Gear Range Selection |
Important: 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. |
• | 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:
• | Diagnostic Trouble Codes (DTCs) that may have set during the testing.
Refer to the applicable DTC. |
• | Scan tool data for any abnormal readings or data. |
Electrical Function Check
Perform this check first, in order to ensure the electronic transmission
components are connected and functioning properly. If these components are
not checked, a simple electrical condition could be mis-diagnosed.
- Connect the scan tool.
- Ensure the gear selector is in PARK and set the parking brake.
- Start the engine.
- Verify that the following scan tool data can be obtained and is
functioning properly.
Refer to
Transmission Scan Tool Data Values
for typical data values. Data that is questionable
may indicate a concern.
• | Transmission input speed (turbine) |
• | Transmission output speed |
• | TFP manual valve position switch |
• | Transmission range (engine list) |
• | Commanded gear (current gear) |
• | PC solenoid reference current |
• | PC solenoid actual current |
• | Engine coolant temperature |
• | Transmission fluid temperature |
• | TCC solenoid duty cycle |
- Monitor the brake switch signal while depressing and releasing
the brake pedal. The scan tool should display:
• | Closed when the brake pedal is released |
• | Open when the brake pedal is depressed |
- Check the garage shifts
6.1. | Apply the brake pedal and ensure the parking brake is set. |
6.2. | Move the gear selector through the following ranges: |
6.2.2. | REVERSE to NEUTRAL |
6.3. | Pause 2 to 3 seconds in each gear position. |
| Important: Harsh engagement may be caused by any of the following conditions:
• | High idle speed. Compare engine idle speed to desired idle speed. |
• | Commanded low PC solenoid current. Compare PC solenoid reference
current to PC solenoid actual current. |
• | A default condition caused by certain DTCs that result in maximum
line pressure to prevent slippage. |
|
| Important: Soft or delayed engagement may be caused by any of the following conditions:
• | Low idle speed. Compare engine idle speed to desired idle speed. |
• | Commanded high PC solenoid current. Compare PC solenoid reference
current to PC solenoid actual current. |
• | Cold transmission fluid. Check for low transmission fluid temperature. |
|
6.4. | Verify the gear engagements are immediate and not harsh. |
- Monitor the transmission range on the scan tool (engine list).
7.1. | Apply the brake pedal and ensure the parking brake is set. |
7.2. | Move the gear selector through all ranges. |
7.3. | Pause 2 to 3 seconds in each range. |
7.4. | Return the gear selector to PARK. |
7.5. | Verify that all of the selector positions match the scan tool
display. |
- Check the throttle angle input.
8.1. | Apply the brake pedal and ensure the parking brake is set. |
8.2. | Ensure the gear selector is in PARK. |
8.3. | Monitor the throttle angle while increasing and decreasing the
engine speed with the throttle pedal. The scan tool throttle angle should
increase and decrease with the engine speed. |
If any of the above checks do not perform properly, record the result
for reference after the completion of the road test.
Upshift Control and Torque Converter Clutch (TCC) Apply
The PCM calculates the upshift points based primarily on two inputs:
the throttle angle and the vehicle speed. When the PCM determines that conditions
are met for a shift to occur, the PCM commands the shift by closing
or opening the ground circuit for the appropriate solenoid.
Perform the following steps:
- Refer to
Shift Speed
.
Choose a throttle position of 10 percent, 25 percent or 50 percent.
All throttle angles shown should be tested to cover the normal
driving range.
- Monitor the following scan tool parameters:
- Place the gear selector in the OVERDRIVE position.
- Accelerate the vehicle using the chosen throttle angle. Hold
the throttle steady.
- As the transmission upshifts, note the vehicle speed when the
shift occurs for each gear change. There should be a noticeable shift feel
or engine speed change within 1 to 2 seconds of the commanded
gear change.
- Compare the shift speeds to the Shift Speed table. Refer to
Shift Speed
. Shift speeds may vary
slightly due to transmission fluid temperature or hydraulic delays
in responding to the electronic controls.
• | Note any harsh, soft or delayed shifts or slipping. |
• | Note any noise or vibration. |
- Repeat steps 1 through 6 to complete all throttle angles.
Important: The TCC will not engage until the engine is in closed loop operation.
The vehicle must be in a near-cruise condition (not accelerating or
coasting) and on a level road surface.
- Check for TCC apply in THIRD and FOURTH gear. Typical apply speeds in
FOURTH gear range from 72 to 88 km/h (45 to 55 mph) depending
on engine size, engine type and axle ratio.
• | Note the TCC apply point. When the TCC applies there should be
a noticeable drop in engine speed and a drop in slip speed to below 100 RPM.
If the TCC apply can not be detected: |
• | Lightly tap and release the brake pedal. The TCC will release
on most applications. |
Part Throttle Detent Downshift
- Place the gear selector in the OVERDRIVE position.
- Accelerate the vehicle to 64-88 km/h (40-55 mph)
in FOURTH gear.
- Quickly increase throttle angle to greater than 50 percent.
- Verify the following:
• | The transmission downshifts immediately to THIRD gear |
Full Throttle Detent Downshift
- Place the gear selector in the OVERDRIVE position.
- Accelerate the vehicle to speeds of 64-88 km/h (40-55 mph)
in FOURTH gear.
- Quickly increase the throttle angle to 100 percent (WOT).
- Verify the following:
• | The transmission downshifts immediately to SECOND gear |
Manual Downshifts
The shift solenoid valves do not control manual downshifts. All manual
downshifts are hydraulic. The solenoid states will change during, or shortly
after, a manual downshift is selected.
Manual 4-3 Downshift
- Place the gear selector in the OVERDRIVE position.
- Accelerate the vehicle to 64-88 km/h (40-55 mph)
in FOURTH gear.
- Release the throttle while moving the gear selector to THIRD.
- Verify the following:
• | The transmission downshifts immediately to THIRD gear |
• | The engine slows the vehicle |
Manual 4-2 Downshift
- Place the gear selector in the OVERDRIVE position.
- Accelerate the vehicle to 64-72 km/h (40-45 mph).
- Release the throttle while moving the gear selector to SECOND.
- Verify the following:
• | The transmission downshifts immediately to SECOND gear |
• | The engine slows the vehicle |
Manual 4-1 Downshift
- Place the gear selector in the OVERDRIVE position.
- Accelerate the vehicle to 48 km/h (30 mph).
- Release the throttle while moving the gear selector to FIRST.
- Verify the following:
• | The transmission immediately downshifts to FIRST Gear. |
• | The engine slows the vehicle. |
Coasting Downshifts
- Place the gear selector in the OVERDRIVE position.
- Accelerate the vehicle to FOURTH gear with the TCC applied.
- Release the throttle and lightly apply the brakes.
- Verify the following:
• | Downshifts occur at speeds shown in the Shift Speed chart. Refer
to
Shift Speed
. |
Manual Gear Range Selection
The shift solenoids control the upshifts in the manual gear ranges.
Perform the following tests using 10 percent to 15 percent
throttle angle.
Reverse
- With the vehicle stopped, move the gear selector to REVERSE.
- Slowly accelerate the vehicle.
- Verify that there is no noticeable slip, noise or vibration.
Manual First
- With the vehicle stopped, move the gear selector to FIRST.
- Accelerate the vehicle to 32 km/h (20 mph).
- Verify the following:
• | There is no noticeable slip, noise, or vibration |
Manual Second
- With the vehicle stopped, move the gear selector to SECOND.
- Accelerate the vehicle to 57 km/h (35 mph).
- Verify the following:
• | The 2-3 shift does not occur |
• | There is no noticeable slip, noise, or vibration |
Manual Third
- With the vehicle stopped, move the gear selector to THIRD.
- Accelerate the vehicle to 64 km/h (40 mph).
- Verify the following:
• | There is no noticeable slip, noise, or vibration |