Toyota Lexusc Owner's Handbook Manual page 26

QUICK REFERENCE
NOTE:
Vehicles with the cruise control: When the cruise control is being used, even if you downshift from "D" or "5" (fifth range) to "4" (fourth
range), engine braking will not be enabled because the cruise control is not cancelled. For vehicle speed reduction, see page 462.
Vehicles with the dynamic laser cruise control: When the cruise control is being used in the conventional (fixed speed) cruise control
mode or in the vehicle-to-vehicle distance control mode, even if you downshift from "D" or "5" (fifth range) to "4" (fourth range), engine
braking will not be applied because the cruise control is not cancelled. For vehicle speed reduction, see pages 473 and 483.
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