What is a Engine Sensor

Hello, I’m Pete from the Car Genius team at RepairPal. I’m sorry you’re dealing with this concern on your Nissan Sentra. Your engine uses multiple sensors for various different components throughout the engine. Those sensors usually send signals to a component like the engine computer itself so the computer can control outputs to the engine or monitor data signals. In some cases a sensor can fail which can cause the failure of an emissions test to where that specific sensor may need to be replaced. There are also drive cycle monitor tests your computer will run that is usually used with emissions testing, with these, the computer monitors certain sensors like the oxygen sensors and EVAP (fuel vapor system) to check for any concerns. Anytime your battery is disconnected, loses charge, or if a fault code is cleared/erased with a scan tool this will restart that drive cycle testing in which the vehicle usually has to be driven for an extended time over days or weeks for that cycle to run and pass or fail throughout various driving conditions and speeds. Keep in mind though that anytime anything is reset in the computer or if you lose battery voltage that testing starts all over again. If there is a specific sensor acting up it would be best to have that sensor properly diagnosed and repaired so the drive cycle can then be completed to pass emissions testing. This is something a reputable shop can help diagnose and pinpoint as well as repair if needed. If you’d like to find a trusted, certified repair shop in your area, you can check here: https://repairpal.com/certified. If you need more advice, or have any further questions about your vehicle, we’re here to help. Just give us a call at 877-913-1554 where we will be happy to assist!