Sensors measure a variety of operating parameters that help to reduce emissions and also serve functions for the engine, transmission and other systems. These sensors generally include the manifold air temperature sensor, coolant temperature sensor, manifold absolute pressure sensor, airflow sensor, throttle position sensor, vehicle speed sensor and oxygen sensors.
All of these sensors provide critical operating information to the vehicle's powertrain control module, the onboard computer that compares the signals from the sensors to programmed values. Based on the signals, the computer then issues commands to various output devices to control the engine and transmission, along with reducing emissions. 1996 and newer vehicles are equipped with second-generation onboard diagnostics (OBDII) systems that put special emphasis on sensor values and emissions.
Sensors do not require regular maintenance or adjustments. Regardless of what a specific sensor measures, all operate within a range of normal values. If a sensor provides a signal outside the normal range long enough, the powertrain control module will set a trouble code, which will usually trigger the SERVICE ENGINE SOON or CHECK ENGINE light. If the light appears, you should have its cause investigated by a professional technician at your earliest opportunity. If the light flashes, the condition is more severe and must be checked out immediately to prevent damage to the catalytic converter.