SPRING-VALVE OUTER 9N5496 - Caterpillar

System Operation Description:The air/fuel ratio control contains two components that work together in order to develop a signal that represents the amount of oxygen in the exhaust.Oxygen Sensor - The oxygen sensor contains a heating element and a sensor. The heating element raises the temperature of the sensor to approximately 700 °C (1292 °F). The electrical resistance of the sensor varies according to the amount of oxygen in the exhaust.Oxygen Buffer - The oxygen buffer performs two functions. The buffer provides electrical power to the oxygen sensor's heating element. The buffer converts the sensor's variable resistance into a variable PWM signal.Five wires run between the buffer and the sensor.VH Wires - The buffer creates a voltage of approximately 11 VDC across the VH wires. This voltage is for the sensor's heating element.VS Wires - The buffer tries to keep the voltage that is across the VS wires at a constant value. The buffer keeps the voltage constant by adjusting the current flow through the IP wires.IP Wire - The amount of current that flows through the IP wire depends on the variable resistance of the sensor. The current will vary from 0 mA at 0 percent of oxygen to approximately 8.7 mA at 21 percent of oxygen.The buffer converts the variable flow of current into a variable PWM signal. The PWM signal that is created by the buffer has a nominal frequency of 500 Hz. The duty cycle of the PWM signal has a range of 30 to 65 percent. The 30 percent corresponds to 0 percent of oxygen and the 65 percent corresponds to 21 percent of oxygen. These values vary slightly between different buffers and sensors. Every new buffer must be calibrated. Calibration is also required according to the engine's Operation and Maintenance Manual, "Maintenance Interval Schedule". Some applications may require more frequent calibration or less frequent calibration.The PWM signal is supplied to the ECM. The ECM uses the signal to maintain the desired emissions levels.The sensor and the buffer provide a wet reading that is slightly lower than a dry reading. The ECM multiplies the wet reading by a conversion factor of approximately 1.25 in order to obtain the reading that is displayed on the electronic service tool. This allows oxygen readings from the service tool to be directly compared to dry readings from an emissions analyzer.The buffer is equipped with a diagnostic circuit that monitors the current flow through the heater via the VH wires. If this current is too low, the buffer assumes that the sensor is disconnected from the buffer or that the sensor has failed. When this occurs, the buffer sets the PWM signal to a duty cycle of approximately 15 percent. The ECM interprets this condition as a diagnostic condition. The ECM will generate a diagnostic code.Electrical power for the buffer is routed through the contacts of a relay. The ECM energizes the relay when the engine is running. The relay may also be energized when the engine is not