Abstract: An internal combustion engine with a closed loop air/fuel ratio control utilizes a heated zirconia sensor, the sensor including a resistance heater element connected to receive electric current from the vehicle battery, the sensor having an internal parasitic capacitance and being characterized by a leakage current path between the heater element and the capacitance. The sensor output voltage is sampled by the closed loop control periodically and current is supplied to the heater element only during periods which end a predetermined time before each such sampling so that any charge on the capacitance may discharge before it affects the sampled voltage. Within each period, the current may be duty cycle modulated in response to vehicle battery voltage to maintain a constant average power to the heater element when heat is required.

Abstract: An apparatus for providing a service reminder when a vehicle has accumulated a predetermined mileage comprises a potentiometer operated by the highest order number wheel of the vehicle odometer to provide an output voltage which changes incrementally with each indexing motion of that number wheel. An electrical detector responsive to the potentiometer output energizes a signal lamp when the output reaches a voltage in a predetermined range representing a desired service interval. An electrical connector in circuit with the potentiometer can be disconnected to change the potentiometer voltage to a value outside the predetermined range to allow the service reminder circuit to turn off the indicator lamp when the indicated service has been performed. The apparatus is adapted to operate in conjunction with an electronic engine control module which can be programmed to detect the predetermined value of the potentiometer output and to operate a signal lamp.