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2. With the ignition OFF, disconnect the 80-way connector at the transmission control module (TCM). 3. Using a fused jumper wire, connect terminal R of the automatic transmission inline 20-way connector to a known good ground. 4. Start the engine and move the range selector to REVERSE position. The transmission should engage REVERSE range. 5. Move the range selector to the D position. The transmission should engage THIRD range. If REVERSE and THIRD range are available in Limp Home Mode, an electrical failure may be Failed clutch Stuck valve Solenoid failure The clutches that could possibly have an indicated failure in Limp Home are the 1-2-3-4 clutch, ROAD TEST The following test provides a method of evaluating the condition of the automatic transmission. Electrical Function Check Upshift Control and Torque Converter Clutch (TCC) Apply Part Throttle Detent Downshifts Full Throttle Detent Downshifts Manual Downshifts Coasting Downshifts IMPORTANT: The Road Test Procedure should be performed only as part of the Functional Test Procedure. Refer to Functional Test.
2008 Chevrolet Silverado 1500 2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
Manual Range Selection REVERSE Manual FIRST Before the road test, ensure the following conditions are met: 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, inspect the following conditions: Transmission fluid level Refer to Transmission Fluid Check. 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 IMPORTANT: Complete the test in the sequence given. Incomplete testing cannot guarantee an accurate evaluation.
2008 Chevrolet Silverado 1500 2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
could be mis-diagnosed. 1. Install the scan tool. 2. Ensure the shift 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 Scan Tool Data List for typical data values. Data that is questionable may indicate a Engine speed Transmission input speed Transmission turbine speed Transmission output speed Vehicle speed TFP 1, 2, 3 and TFP 4 pressure switch states C, D, E and REVERSE pressure switch states Transmission range, engine list 4WD low Commanded range, current range PCS1 and PCS2 solenoid reference current PCS1 and PCS2 solenoid actual current PCS1 and PCS2 solenoid duty cycle Brake switch Engine coolant temperature Transmission fluid temperature Throttle angle Ignition voltage Shift solenoid 1 Shift solenoid 2 Shift solenoid 3 Modulated main G solenoid TCC solenoid duty cycle TCC slip speed 5. Monitor the brake switch signal while depressing and releasing the brake pedal. The scan
2008 Chevrolet Silverado 1500 2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
tool should display the following: Closed when the brake pedal is released Open when the brake pedal is depressed 6. Check the garage shifts. 1. Apply the brake pedal and ensure the parking brake is set. 2. Move the shift selector through the following ranges: 1. PARK to REVERSE 2. REVERSE to NEUTRAL 3. NEUTRAL to DRIVE 3. Pause 2 to 3 seconds in each selector 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 PCS1 or PCS2 solenoid current Compare PCS1 and PCS2 solenoid reference current A default condition caused by certain DTCs that Shift is not fully adapted 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. Low fluid level Cold transmission fluid Inspect for low transmission fluid temperature.
2008 Chevrolet Silverado 1500 2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
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