Abstract: A self-diagnosis system for the exhaust gas recirculation control system of an internal combustion engine comprises a recirculation pipe for returning the exhaust gas to the intake manifold, switching unit for opening or closing the recirculation pipe, control unit for controlling the switching operation of the switching unit, operating conditions detector for detecting the operating conditions of the engine, storage unit for storing the detection values of the detector separately when the switching unit opens and closes, decision unit supplied with the detection values from the storage unit for deciding whether the difference therebetween is in a predetermined range, and an alarm unit for issuing an alarm when the decision unit decides that the difference of the detection values is in the predetermined range, thus making stable self-diagnosis possible with a simple configuration.

Abstract: In an engine preheating control system, in which the temperature of glow plugs mounted in a diesel engine is held in a constant high temperature range during the cranking operation after the closure of an engine key switch through the control of power supply to the glow plugs based upon the detection of changes of the resistance of the glow plugs, a main relay for controlling the power supply from a power supply source through a current detecting resistor to the glow plugs and a sub-relay for controlling power supply through a stable preheating resistor and the detecting resistor to the glow plugs are energized and de-energized in response to first to fourth control signals.

Abstract: A revolution control circuit for an internal combustion engine comprising a speed voltage generator for generating a speed voltage in accordance with the number of revolutions of the engine, an oscillator circuit which starts to oscillate when the speed voltage becomes higher than a predetermined value, a transistor circuit for causing electrical semiconductor elements to be turned on and off intermittently in accordance with the oscillation frequency of the oscillator circuit, and a control element for increasing and decreasing the quantity of fuel injected in synchronism with the on and off operations of the transistor circuit.