MDK Emergency Operation

If a fault is detected in the system, the modes of operation are emergency operation 1 and emergency operation 2.

Emergency operation 1 involves activation of the EML warning lamp, MDK deactivated, the throttle valve is opened mechanically by the springs and throttle cable, MDK opening is compensated for by closing the idle speed actuator and retarding the ignition (engine power reduction) and engine power is further limited by fuel injector cutout. Emergency operation 1 limits the dynamic operation if one or more of the potentiometers fail. The engine can slowly reach maximum speed with limited power. The EML light will be illuminated to alert the driver of a fault.

If another fault is encountered in addition to emergency operation 1 or if the plausibility is affected, emergency operation 2 is activated by the PCM. An example of plausibility fault would be that the pulley position does not match the MDK position and the associated airflow. Emergency operation 2 can also be initiated by simultaneously pressing both the accelerator pedal and the brake pedal, or if a fault is encountered in the brake light switch diagnosis. When in emergency 2 operation mode, there is an engine speed limitation (slightly above idle speed) in addition to the measures for emergency operation 1. In emergency operation 2, the engine speed is always limited to 1300 RPM if the brake is not applied, and approximately 1000 RPM if the brake is applied. The vehicle speed is limited to approximately 20-25 mph. The reason for limiting the vehicle speed is if the MDK is wide open and vacuum assist is insufficient for the brakes. The emergency operation functions are inactive when ignition is switched off, main relay is deactivated, and engine is started again.

MDK safety concept can detect a jammed or binding throttle valve as well as a broken link spring. This fault is detected by the PCM monitoring the feedback potentiometers from the MDK in relation to pulse width modulation to activate the MDK motor. Emergency operation functions if the throttle valve is jammed. In the event of a fault, the DIS or MoDiC must be used to interrogate the fault memory, and clear the fault once the proper repair has been performed.