Important: 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 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. |
• | 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, inspect for the following:
• | Transmission fluid level |
• | 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
Scan Tool Data List
for typical data values. Data that is questionable may indicate
a concern.
• | Transmission output speed |
• | Transmission range (engine list) |
• | PC solenoid reference current |
• | PC solenoid actual current |
• | Engine coolant temperature |
• | Transmission fluid temperature |
• | Acceleration Pedal Position |
• | TCC solenoid duty cycle |
- Monitor the brake switch signal while depressing and releasing the brake
pedal. The scan tool should display:
• | Open when the brake pedal is released. |
• | Closed when the brake pedal is depressed. |
- Check the garage shifts.
6.1. | Apply the brake pedal and ensure that 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. |
6.4. | Verify the gear engagements are immediate and not harsh. |
Important: Harsh engagement may be caused by any of
the following conditions:
| 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:
| 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 |
| Inspect for low transmission fluid
temperature. |
- Monitor 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 2-3 seconds in each range. |
7.4. | Return gear selector to PARK. |
7.5. | Verify that all selector positions match the scan tool display. |
- Check accelerator pedal input.
8.1. | Apply the brake pedal and ensure that the parking brake is set. |
8.2. | Ensure the gear selector is in PARK. |
8.3. | Monitor accelerator pedal while increasing and decreasing engine speed
with the throttle pedal. The scan tool accelerator pedal 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 two inputs: throttle
angle and vehicle speed. When the TCM determines that conditions are met for a shift
to occur, the TCM commands the shift by closing or opening the ground circuit for
the appropriate solenoid.
Perform the following steps:
- Refer to the
Shift Speed
table
in this section and choose a throttle position of 12 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 electronic controls.
• | Note any harsh, soft or delayed shifts or slipping. |
• | Note any noise or vibration. |
- Repeat steps 1-6 to complete all throttle angles.
Important: This transmission is equipped with an electronically
controlled capacity clutch (ECCC). The pressure plate does not fully lock to the torque
converter cover. The pressure plate maintains a small amount of slippage, approximately
20 RPM, in THIRD, FOURTH and FIFTH gears, depending on the vehicle application.
ECCC was developed to reduce the possibility of noise, vibration or chuggle caused
by TCC apply. Typical apply speeds are 49-52 km/h (30-32 mph)
in THIRD gear and 65-73 km/h (40-45 mph) in FOURTH gear.
Full lockup is available at highway speeds on some applications.
Important: The TCC will not engage until the engine
is in closed loop operation and the vehicle speed is as shown in the Shift Speed table.
Refer to
Shift Speed
. The vehicle must be
in a near-cruise condition, not accelerating or coasting, and on a level road
surface.
- Inspect for TCC apply in THIRD, FOURTH and FIFTH gear.
• | 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: |
• | Refer to the
Shift Speed
table
for the correct apply speeds. |
• | 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 FIFTH gear.
- Quickly increase throttle angle to greater than 50 percent.
- Verify the following:
• | The transmission downshifts immediately to FOURTH gear |
- Place the gear selector in the OVERDRIVE position.
Full Throttle Detent Downshift
- Accelerate the vehicle to speeds of 64-88 km/h (40-55 mph)
in FIFTH gear.
- Quickly increase throttle angle to 100 percent (WOT).
- Verify the following:
• | The transmission downshifts immediately to THIRD gear |
Manual Downshifts
The shift solenoid valves control the initial downshift for the 5-4,
4-3, 3-2 manual downshifts. The solenoid states should change during
or shortly after a manual downshift is selected.
Manual 5-4 Downshift
- Place the gear selector in the OVERDRIVE position.
- Accelerate the vehicle to 64-88 km/h (40-55 mph)
in FIFTH gear.
- Release the throttle while moving the gear selector to FOURTH.
- Verify the following:
• | The transmission downshifts immediately to FOURTH gear |
• | The engine slows the vehicle |
Manual 5-3 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 THIRD.
- Verify the following:
• | The transmission downshifts immediately to THIRD gear. |
• | The engine slows the vehicle. |
Manual 5-2 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 SECOND.
- Verify the following:
• | The transmission downshifts immediately to SECOND gear. |
• | The engine slows the vehicle. |
Coasting Downshifts
- Place the gear selector in the OVERDRIVE position.
- Accelerate the vehicle to FIFTH 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 table. Refer to
Shift Speed
. |
Manual Gear Range Selection
The shift solenoids control the upshifts in the manual gear ranges.
Perform the following tests using 10-15 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 Second
- With the vehicle stopped, move the gear selector to SECOND.
- Accelerate the vehicle to 32 km/h (20 mph).
- Verify the following:
• | The TCC does not apply. |
• | There is no noticeable slip, noise, or vibration. |
Manual Third
- With the vehicle stopped, move the gear selector to THIRD.
- 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 Fourth
- With the vehicle stopped, move the gear selector to FOURTH.
- Accelerate the vehicle to 64 km/h (40 mph).
- Verify the following:
• | There is no noticeable slip, noise or vibration |
Driver Shift Control
The floor shift control is located in the center console assembly. It contains
the upshift and downshift switches for the driver shift control system. The driver
shift control system is activated when the floor shift control lever is moved to the
right into the manual position from the drive position. When the manual position is
selected, an upshift is requested by pushing the floor shift control lever forward
to the + position and a downshift is requested by pulling the floor shift control
lever to the - position. When an upshift or a downshift is requested, a signal
is sent to the TCM which commands the shift solenoids ON or OFF to achieve the appropriate
gear.