No Engine Braking In "2"
WARNING: This page is about a different car, the 2002 Mazda MPV. However, it is still accessible from the selected car via links, so may be relevant.
Possible cause: clutch slipped or burned (reduction brake), line pressure low, faulty VSS, faulty input/turbine speed sensor, faulty sensor ground, faulty control valve body, O/D OFF switch (short, or open circuit, poor operation).