• | Perform the road test using the Scan Tool. |
• | Perform this test only when traffic and road conditions permit. |
• | Observe all traffic safety regulations. |
Conduct the test according to the following steps:
- Start the engine.
- Depress the brake pedal.
- Move the gear selector between the following positions:
Important: Transmission shifts should be immediate and not harsh.
Use the scan tool in order to see if any transmission malfunction codes
have been set. If so, refer to
Functional Test
.
After repairing the vehicle, perform the road test and verify that no codes
have been set again.
If no codes have been set and the condition remains, refer to the Diagnostic
Tables.
If the transmission is not performing well and no trouble codes have
been set, check for an intermittent condition. Check all electrical connections
for damage or a loose fit. Some scan tools have a snapshot test which can
help to catch an intermittent condition that does not occur long enough in
order to set a code.
If the condition is suspected to originate in the torque converter,
refer to
Torque Converter Clutch Diagnosis
.
Electrical/Garage Shift Test
Perform this test before a road test in order to make sure that electronic
control inputs are connected and operating. If you do not check the inputs
before operating the transmission, you could misdiagnose a simple electrical
condition as a major transmission condition.
A scan tool provides valuable information. Use the scan tool on the
Hydra-Matic 4L80-E transmission for accurate diagnosis.
- Move the gear selector to Park (P) and set the parking brake
- Connect the scan tool to the DLC terminal
- Start the engine
- Connect power to the scan tool
- Verify that the following signals are present on the scan tool:
• | Transmission Input (Shaft) Speed Sensor (A/T ISS) |
• | Transmission Output (Shaft) Speed Sensor (A/T OSS) |
• | Automatic Transmission Fluid Pressure Manual Valve (TFP Val.)
Position Switch |
• | Vehicle speed (MILES/HOUR) |
• | Reference Transmission Pressure Control Solenoid Amperage (REF
CURRENT) |
• | Actual Transmission Pressure Control Solenoid Amperage (ACT CURRENT) |
• | Engine Coolant Temperature (ECT) |
• | Automatic Transmission Fluid Temperature (TFT) Sensor |
• | TCC Duty Cycle (TCC DC) |
- Monitor the TCC BRAKE signal with the scan tool while tapping
the brake pedal with your foot. The brake switch signal should be:
VCM
• | CLOSED - when the brake pedal is released |
• | OPEN - when the brake pedal is depressed |
PCM
• | OPEN - when the brake pedal is released |
• | CLOSED - when the brake pedal is depressed |
- Monitor the Automatic Transmission Fluid Pressure Manual Valve
Position Switch (TFP Switch) signal by moving the gear selector through all
of the ranges. Verify that the TFP Switch state matches the gear range which
is indicated on the instrument panel or on the console. Gear selections should
be immediate and not harsh.
- Move the gear selector to Neutral and monitor the Throttle Position
Angle while increasing and decreasing engine RPM with the accelerator pedal.
The Throttle Position Angle should increase with the engine RPM.
Upshift Control and Torque Converter Clutch (TCC) Apply
The vehicle computer calculates the upshift points based primarily upon
two inputs:
• | Throttle Position Angle |
When the VCM/PCM indicates that a shift should occur, an electrical
signal is sent to the shift solenoids, which in turn move the valves to perform
the upshift.
The shift speed charts refer to THROTTLE POSITION ANGLE instead of MIN
THROTTLE or WOT in order to make shift speed measurement more uniform and
accurate. Monitor THROTTLE POSITION ANGLE by using the scan tool.
Some scan tools have been programmed in order to measure and record
shift point information. Check the instruction manual in order to see if this
test is available.
With gear selector in D4, perform the following steps:
- Refer to
Shift Speed
and
choose a throttle position of either 15% or 20%.
- Monitor the throttle position with the scan tool.
- Accelerate to the chosen throttle position. Hold the throttle
steady.
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.
- As the transmission upshifts, note the shift speed for each of
the following gears:
- The Torque Converter Clutch (TCC) should apply in Third or Fourth
gear. The TCC will not apply unless the engine coolant has reached a minimum
operating temperature of approximately 54°C (130°F). Note when the
TCC applies. If you do not notice the apply by an RPM drop, refer to
Torque Converter Clutch Diagnosis
.
- 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 throttle angle. Verify the following
results:
• | The transmission downshifts to 3rd gear immediately. |
• | The 1-2 Shift Solenoid valve turns OFF. |
Full Throttle Detent Downshift
At vehicle speeds of 64-88 km/h (40-55 mph)
in Fourth gear, quickly increase the throttle angle to its maximum position.
Verify the following results:
• | The transmission downshifts to 2nd gear immediately. |
• | The 1-2 and 2-3 Shift Solenoid valves turn OFF. |
Manual Downshifts
The shift solenoid valves do not control the initial downshift during
manual downshifts. All manual downshifts are hydraulic. The solenoid states
will change during, or shortly after, a manual downshift is selected.
- At vehicle speeds of 64-88 km/h (40-55 mph)
in Fourth gear, release the accelerator pedal while moving the gear selector
to D3. Observe the following results:
• | The transmission downshifts to Third gear immediately |
• | The engine slows the vehicle down |
- Move the gear selector back to D4 and accelerate to 64-72 km/h
(40-45 mph). Release the accelerator while moving the gear selector
to D2 and observe the following results:
• | The transmission immediately downshifts to Second gear |
• | The engine slows the vehicle down |
- Move the gear selector back to D4 and accelerate to 48 km/h
(30 mph). Release the accelerator pedal while moving the gear selector
to D1 and observe the following results:
• | The transmission immediately downshifts to First gear immediately |
• | The engine slows the vehicle down |
Coasting Downshifts
- With the gear selector in D4, accelerate to Fourth gear with the
TCC applied.
- Release the accelerator pedal and lightly apply the brakes. Observe
the following results:
• | Downshifts occur at speeds shown on 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 by accelerating at 10-15 degrees TPS.
Manual Third (D3)
With the vehicle stopped, move the gear selector to D3 and accelerate
in order to observe the following conditions:
Manual Second (D2)
• | With the vehicle stopped, move the gear selector to D2 and accelerate
in order to observe the 1-2 shift. |
• | Accelerate to 56 km/h (35 mph) and observe the following
conditions: |
- | The 2-3 shift does not occur. |
- | The TCC does not apply. |
Manual First (D1)
With the vehicle stopped, move the gear selector to D1. Accelerate to
32 km/h (20 mph) and observe the following conditions:
• | The TCC does not apply. |
Reverse (R)
With the vehicle stopped, move the gear selector to R and slowly accelerate
in order to observe that the 1-2 Shift Solenoid valve is ON.