"Check Engine" lamp in the instrument cluster is turned on by the computer that is located in the vehicle some place. The responsibility of this computer is to keep an eye on all the sensors that are working in the engine compartment. As this computer makes its rounds to check on each of the sensors, and if it finds one misbehaving, the computer turns on the “Check Engine” lamp to let the driver know that some sensor is misbehaving. A constant log of these events is kept by the computer. When a technician hooks up his laptop to the car computer he can read the complete log written by the event. Based on the log the technician can then approach the failing sensor and check its values. Once the investigation is complete and then a corrective action can be implemented. The cost and cause of finding a non performing sensor is $135.00. A cost of corrective action is presented after the evaluation is complete. Required evaluation time is generally two days.