Electronically actuated transmission range control system

A control system for a multiple-ratio automatic transmission for an engine-driven vehicle, the transmission having gearing and pressure-operated clutches and brakes for controlling the gearing to define a range of forward drive ratios, a reverse drive mode and a park mode, the control system comprising:

• range and ratio solenoid actuators for controlling pressure distribution to the transmission clutches and brakes;
• a driver controlled transmission range selector including a selector position sensor, the position sensor having a multiple digital bit output signal, a forward drive range being characterized by a first digital number and reverse drive mode being characterized by a second digital number;
• an electronic controller for the transmission, the controller having signal input conditioning circuits communicating with the selector position sensor and output driver circuits communicating with the solenoid actuators;
• and
• a control module forming a part of the electronic controller and having a memory register with programmed digital numbers corresponding to reverse mode and to forward drive range;
• the control module including means for comparing the selector position output signals with the programmed digital numbers to detect an error in the digital numbers indicating a fault in the selector position;
• fault detection feedback means for alerting the driver of the presence of a selector position sensor fault;
• the control system having a solenoid power cutoff relay electrically connected to the output driver circuits and the solenoid actuators for controlling delivery of power to the solenoid actuators in response to the detection of two or more errors in the digital numbers developed by the range selector position sensor.