December 12, 2022
Troubleshooting GM 8L45, 8L90 No Move & No Pressure Conditions
Jim Mobley
GM 8L90 Model Year 2019 S4/23468 Control Valve Changes
Engine controls/management for model year 2019 GM 8L90 transmissions in truck and SUV applications with 5.3 and 6.2L V-8 engines made a change from active fuel management (AFM) to dynamic fuel management (DFM). AFM controls would convert a V-8 engine into a four-cylinder under lighter engine load and cruising conditions. DFM controls allow engine management to deactivate any of the eight cylinders selectively to help improve fuel mileage and emissions.
This change also affected the torque converter and the valve body assembly in the 8L90. The torque converter is now equipped with a centrifugal pendulum absorber. GM associates its attributes with a dual-mass flywheel to help dampen noise and vibration.
The valve body in the 8L90 applications also went through a change involving the control solenoid, valve body casting and control valve. Sonnax S2/S3/S4/TCC clutch control valve kit 154740-11K contains a .443" dia. valve that cannot be used in the ’19-later S4 location or shift complaints will occur. This valve assembly also is found in Sonnax Zip Kits 8L45-8L90-TCC-ZIP and 8L45-8L90-TCC-ZIP.
Here are three ways to identify whether you have a previous-design or new-design unit.
| Figure 1 - Model Year 2019 8L90 External Identification |
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An external ID can be seen without valve body disassembly. Note the triangle on the canister. |
| Figure 2 - 8L90 S4 Control Valve Changes |
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Shown here is the previous-design S4 control valve and solenoid compared to the new design. Note the previous-design control valve has two diameters and the new design only has one. |
| Figure 3 - 8L90 Previous Design Oil Circuit |
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This diagram shows an oil circuit from the previous design. The late design valve is still plumbed the same way, but the diameter change and the new-design solenoid may provide better control of the 1-2 upshift, especially when DFM is activated. |
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