Abstract: A tester is disclosed for any one of three different types of cruise control systems on a vehicle, each of which has a cruise engage signal conductor which is tested for circuit continuity. The continuity testing circuit includes a battery, light emitting diode (LED) and a transistor with its base connected through a bias resistor to a connector element which is connected to the cruise engage signal conductor for testing its continuity. The circuit continuity is indicated by turn-on of the LED for two types of cruise control systems and by failure to turn-on the LED for the third type of cruise control system.

Abstract: A tester for a vehicle engine idle air control system includes an air bypass valve operated by a solenoid which receives a pulse width modulated signal to control the degree of opening of the valve. The tester is inserted in the vehicle wiring harness and includes a manually controlled pulse width modulator for generating a test voltage to the solenoid. A switch is connected within the tester to switch between engine computer control or manual modulator control of the solenoid. A bar graph display monitors the voltage supplied to the solenoid to indicate the magnitude thereof. The bar graph display also indicates the occurrence of short or open circuits.

Abstract: A combined stepper motor tester and pulse train monitor is disclosed for use with a vehicle engine idle air control system. The motor tester comprises a driver pulse generator for generating a pair of pulse trains for energizing the two coils of a stepper motor. It is provided with a manually actuated switch for controlling the phase sequence and time duration of the pulse trains applied to the motor. The operation of the motor by the motor tester, with the vehicle engine running, causes the engine computer module to generate a pair of pulse trains in response to the changing engine conditions. A pulse train monitor, plugged into the output of the engine control module includes a pair of bi-polar LEDs, one for each of the pulse trains generated by the engine control module. The bi-polar LED for each pulse train will alternately flash without both LEDs being off at the same time in response to an uninterrupted pulse train.