Special Testing Procedures
Special Testing Procedures
Special Tool(s):
The special tests are designed to aid the technician in diagnosing the hydraulic and mechanical portions of the transmission.
Engine Idle Speed Check
Refer to Computers and Control Systems for diagnosis and testing of the engine idle speed.
Line Pressure Test
CAUTION: Carry out the Line Pressure Test prior to carrying out the Stall Speed Test. If line pressure is low at stall, do not carry out the Stall Speed Test or additional transmission damage will occur. Do not maintain wide-open throttle (WOT) in any transmission range for more than 5 seconds or transmission damage may occur.
CAUTION: Apply the parking brake and block drive wheels during the line pressure test. Vehicle movement during the test may cause personal injury or damage to the vehicle and equipment.
NOTE: Certain sensor failures may cause high control pressure and failure mode effect management (FMEM) actions. Make sure that on-board diagnostic and electrical repairs have been carried out, or test results may be incorrect.
This test verifies the line pressure is within specifications.
1. Connect the Pressure Gauge to the line pressure tap.
2. Start the engine and check the line pressures at idle speeds with the transmission in each gear range. Refer to the Line Pressure Chart to determine if the line pressure is within specification.
CAUTION: Do not immediately press the throttle to the floor or allow the throttle to immediately close, or internal damage to the engine or transmission will occur.
3. Check line pressure at wide open throttle (WOT) stall speed with the range selector lever in all gear ranges. Slowly press the throttle to WOT record the pressure reading. After recording the pressure reading slowly release the throttle until closed throttle is obtained (idle). Refer to the Line Pressure Chart to determine if the line pressure is within specification.
4. If pressure is not within specification, refer to the Line Pressure Chart for further diagnosis.
Stall Speed Test
WARNING: Apply the service and parking brakes firmly while carrying out each stall test.
CAUTION: Carry out the Line Pressure Test prior to carrying out the Stall Speed Test. If line pressure is low at stall, do not carry out the stall test or additional transmission damage will occur. Do not maintain wide open throttle (WOT) in any gear range for more than five seconds.
CAUTION: After testing each of the ranges, move the range selector into the NEUTRAL position and run the engine at 1,000 rpm for about 15 seconds to allow the torque converter to cool off before continuing onto the next range.
CAUTION: If the engine speed recorded by the tachometer exceeds maximum specified rpm, release the throttle immediately. Clutch or band slippage is indicated.
NOTE: The stall test should only be carried out with the engine and transmission at normal operating temperatures.
NOTE: Prolonged use of this procedure may set DTCs P0712 or P1783. After carrying out the stall speed test, run on-board diagnostics and clear the DTCs.
The stall test checks the operation of the following items:
- Torque converter clutch (TCC)
- Forward clutch
- Low one-way clutch
- Overdrive one-way clutch
- Engine driveability concerns
1. Connect a tachometer to the engine.
2. Press the accelerator pedal to floor (WOT) in each range. Record the rpm reached in each range. Stall speeds should be in the appropriate range.
Air Pressure Tests
A no-drive condition can exist, even with correct transmission fluid pressure, because of inoperative clutches or bands. Refer to the Band/Clutch Application Chart to determine the appropriate elements. A clutch concern can be located through a series of checks by substituting air pressure for fluid pressure to determine the location of the concern.
Example: When the transmission range selector lever is in a forward gear range ((D), 2, 1), a no-drive condition may be caused by an inoperative forward clutch.
1. Drain the transmission fluid. Remove the transmission fluid pan.
2. Remove the filter and seal assembly, the solenoid body, the control assemblies and separator plate, upper/lower gaskets.
3. The inoperative clutches can be located by applying air pressure into the appropriate clutch port. See the Air Pressure Test Port Locations illustration for clutch port locations.
4. Apply air pressure to the appropriate clutch port (see the Air Pressure Test Port Locations illustration). A dull thud may be heard or movement felt when a clutch piston is applied. If the clutch seals or check ball are leaking, a hissing may be heard.
5. If the clutches fail to operate during the air check:
- inspect the fluid passages in the case.
- the piston seals are not seated, not installed or are damaged.
- plugged feed holes for clutch apply in the case and/or clutch cylinder.
- damaged piston and/or clutch cylinder.
6. Repair as required and recheck.