Q: Which sensors are most important for monitoring and improving the engine’s performance?

The way modern electronic engine control systems are designed, all of the sensors are important but some are more crucial to the vehicle than others. For example, if the engine electronic control unit (ECU) loses the input from the coolant temperature sensor, the engine will probably keep running, although not optimally. The car’s Malfunction Indicator Light (Check Engine Light or Service Engine Soon Light) will come on letting you know there’s something related to the engine controls that needs attention. On the other hand, if the crankshaft position sensor fails, the engine won’t run because the ECU absolutely needs its input to know when to fire the spark plugs and fuel injectors. Modifying individual sensors to improve fuel mileage or get a little power boost without detrimentally affecting emissions and/or drivability is very difficult outside an engineering/laboratory setting.