GM Service Manual Online
For 1990-2009 cars only

No 2-1 Downshift

Checks

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DEFINITION: No second gear to first gear downshift

External Automatic Transmission Control Valve Body Assembly (39)

    • Reverse, 1st Shift Solenoid Valve Assembly (S1) (310)
    • 2--3, 3-4 Shift Solenoid Valve Assembly (S2) (308)
    • 1-2, 2-3, Reverse Shift Solenoid Valve Assembly (S3) (300)
    • 3-4, 4-5 Shift Solenoid Valve Assembly (S4) (303)

Verify that all solenoids respond electrically. If there is no response, perform an electrical diagnosis. If there are no electrical concerns, remove the solenoid valve assemblies as needed, and inspect the solenoid O-ring seals, and the solenoid bores for signs of damage and/or missing seals. If the solenoid valves responded electrically and there are no bore or seal concerns, replace the solenoid valve assemblies as necessary due to possible internal mechanical concerns and retest. If a condition is still present after replacing the solenoid valve assembly, replace the complete automatic transmission control valve body assembly (39).

Internal Automatic Transmission Control Valve Body Assembly (39)

    • M1 Shift Valve (389)
    • M2 Shift Valve (426)
    • U1 Shift Valve (386)
    • U2 Shift Valve (392)

Remove the automatic transmission control valve body assembly (39) and inspect the items listed. Inspect the internal bores and the valves for signs of wear and/or damage, including internal contamination. If unable to verify any repairable concerns, replace the complete automatic transmission control valve body assembly (39).

Clutch - Mechanical/Hydraulic

Front Internal Gear and Low Clutch Sprag Assembly (25)

Remove the automatic transmission case cover and 1-2 reverse clutch assembly (19), the forward and direct clutch assembly (23), and the front carrier sun gear assembly (24) to gain access to the front internal gear and low clutch sprag assembly (25). Disassemble the front internal gear and low clutch sprag assembly (25) in order to inspect and clean. Repair or replace components as necessary to correct the condition.