A particulate matter (PM) sensor circuit arrangement includes a PM sensor. The sensor includes, integral therewith, a PM sensor resistor, a resistive temperature device (RTD) resistor, and a heater resistor. The PM sensor includes four terminal pins, of which a) a first terminal pin is connected to one terminal of the PM sensor resistor; a second terminal pin is connected to one terminal side of said RTD resistor; c) a third terminal pin being connected to one terminal of a heater resistor; and d) a fourth common terminal pin is connected to respective opposite terminals of the PM sensor resistor, RTD resistor, and heater resistor to the first, second, and third terminal pins. The fourth common terminal pin is operationally connected to a boost or voltage supply and the first pin is connected to a low side line.

A gas sensor including a detection element section (71) including a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body, and a heater (73) for heating the detection element section (71). Inherent characteristic information is recorded in a record section (170) provided on the gas sensor or a record section provided separately from the gas sensor. The inherent characteristic information is information specific to the detection element section (71) and which allows setting of a relation between a change in the temperature of the detection element section (71) and a change in the internal resistance between the pair of electrodes.

A sensor element includes: an element base including: a ceramic body made of an oxygen-ion conductive solid electrolyte, and having a gas inlet at one end portion thereof; at least one internal chamber located inside the ceramic body, and communicating with the gas inlet under predetermined diffusion resistance; an electrochemical pump cell including an electrode located on an outer surface of the ceramic body, an electrode facing the chamber, and a solid electrolyte located therebetween; and a heater buried in the ceramic body, and an leading-end protective layer being porous, and covering a leading end surface and four side surfaces in a predetermined range of the element base on the one end portion. The leading-end protective layer has an extension extending into the gas inlet, and fixed to an inner wall surface of the ceramic body demarcating the gas inlet.

A controller is used for an air-fuel ratio sensor. The air-fuel sensor includes a detection element that detects an oxygen concentration, and a PWM-controlled heater that receives a PWM signal for temperature control of the detection element. The controller includes a resistance detection circuit configured to detect a resistance of the detection element, and a processor. The processor is programmed to generate the PWM signal for the heater based on the detected resistance such that the resistance of the detection element is kept at a predetermined target resistance, and determine whether a failure has occurred in the air-fuel ratio sensor based on a manner of time-series increase in duty cycle of the PWM signal.

A control device selectively executes first and second energization control for controlling an energization amount to the heater. The first energization control is executed to keep temperature of a sensor element within an active temperature region. The first energization control is PWM control in which the energization amount is controlled with closed loop control such that an impedance of the sensor element matches a target value. The second energization control is PWM control in which the energization amount is controlled with open loop control so as to keep the temperature of the sensor element within a preset temperature region that is lower than the active temperature region. The control device executes the second energization control during an internal combustion engine is stopped while executing the first energization control during the internal combustion engine is not stopped.

Methods and systems are provided for a NO.sub.x sensor. In one example, a method includes heating a NO.sub.x sensor during a vehicle off in response to a cumulative heat energy applied to the NO.sub.x.

Systems, devices, methods and programs for reducing emissions from engines are provided. For example, one system for reducing emissions from engines comprises a heating controller coupled to an energy storage device (ESD). The heating controller is configured to control a heating element to heat one or more components of an after-treatment system using energy from the ESD under a first condition and to control the heating element to stop heating the one or more components of the after-treatment system when a second condition is satisfied. Additionally, another system for reducing emissions from engines comprises a controller detecting a decrease in a demanded torque from an engine and an ISG. The controller is then configured to operate a clutch to disengage the engine from the ISG, if after removing fuel from the engine, the sensed speed of the engine is above a threshold.

A gas sensor includes a sensor element body having a porous layer provided on an outer surface, and a power supply device which supplies power to a heater element that is in the sensor element body. The amount of power being applied to the heater element by the power supply device when gas detection is being performed by the gas sensor in a steady state is designated as P [W], the volume of the length range of a heating region of the heater element provided in the sensor element body as V [mm.sup.3], and the applied power density as X [W/mm.sup.3], where X is a value expressed by P/V. In that case, the following relationship is satisfied between the applied power density X and the average thickness Y [μm] of the porous layer:

Y≥509.32−2884.89X+5014.12X.sup.2

A sensor system for an engine for which an automatic stop-restart control is performed, the sensor system including: an exhaust gas sensor including a heater that heats a sensor element; and a control unit configured to: while the engine is stopped by the automatic stop-restart control, execute a preheat control of adjusting a temperature of the sensor element to a preheat temperature lower than an activation temperature; when an automatic start condition is satisfied, stop the preheat control and increase the temperature of the sensor element to the activation temperature; when an automatic stop condition is satisfied and a delay condition has not been satisfied, set the preheat temperature to a first temperature; and when the automatic stop condition is satisfied and the delay condition has been satisfied, set the preheat temperature to a second temperature higher than the first temperature.

It is to determine whether a temperature rise condition of a first cell or a second cell is satisfied based on whether a first parameter has exceeded a predetermined first threshold or a second parameter has exceeded a predetermined second threshold. After satisfaction of the temperature rise condition, it is to determine that an exhaust gas sensor is in an active state upon determination that a corresponding time condition is satisfied.