Abstract: A vehicle engine includes an exhaust monitoring system with an exhaust mounted oxygen sensor and apparatus for processing the sensor output voltage into an exhaust constituent signal which may, for example, be used to control the air-fuel ratio of the engine fuel supply to a substantially stoichiometric ratio, the apparatus including a low pass filter which suppresses components of the signal greater in frequency than a predetermined cutoff frequency. An alternating voltage generator effective to generate a square wave of at least the cutoff frequency is connected through a reference impedance, a capacitor and the oxygen sensor in series to ground, thus creating a voltage divider with an output between the reference impedance and the sensor internal impedance, the voltage at the output having a peak-to-peak amplitude which varies inversely with sensor temperature. The voltage at the output is provided to a peak detector, which generates therefrom a signal representing the temperature of the oxygen sensor.

Abstract: A circuit for energizing a fuel injector valve coil in response to a fuel injection pulse including a storage capacitor which is charged from a relatively high voltage source and which is discharged through the fuel injector valve coil through a controlled rectifier gated conductive upon the initiation of a fuel injection pulse signal. The charging circuit for the capacitor is disabled upon initiation of capacitor discharge for a time period at least greater than the time for the capacitor discharge current to decrease to a value to effect commutation of the controlled rectifier after which capacitor charging is reinitiated. A holding circuit is provided for holding the fuel injector valve coil energized for the duration of the fuel injection pulse signal.