B Series Truck 2WD L4-2184cc 2.2L 2200 2-bbl (1990)
Control Module: Description and Operation
The EC-AT (electronically controlled automatic transmission) Control Unit, located under the dash left of the steering column, is the control unit for
various electrically operated functions of the R4AX-EL automatic transmission. One of these functions is torque converter lockup or lockup inhibit,
activated according to operating conditions. Control of ATF flow to the torque converter and lockup are achieved by EC-AT control unit energizing and
de-energizing the lockup solenoid on the transmission. The ATF passage is closed when current is applied and open when it is cut off.
To coordinate engine operating conditions with transmission functioning, the ECU sends a signal to the EC-AT control unit (an output from the ECU).
The signal informs the control unit of engine throttle position, an input used to calculate lockup control. Lockup is permitted during most driving
conditions but specifically inhibited when the 4 A/T control unit receives a wide open throttle signal from the ECU.
NOTE: Mazda manuals also refer to the EC-AT control unit as the HAT (hydraulically-controlled automatic transmission) control unit.
