You know I have watched a lot of people try and diag there own car problem , but most get a intiminated right from the start! Because they are overthinking the problem, they are looking under the hood at all of these things!switches relays wires bolts nuts everything looks complicated .. But the truth is everything they are looking at will most likely never will be the problem ! Ofcourse the car is a complicated piece of technology , you don’t have to know what everything does ! You have to look at the immediate problem . Now do some research find out what usually is related to the issue. That puts you on the hunt.there is YouTube best thing ever invented ,google now chat gpt. So much free info available! Now you have an idea what the issue is , time to pull some codes . Codes won’t tell you what the problem is only test tell that! But codes can steer you in the right direction ! We as in technicians don’t change the sensor because it has a code.we diagnose what caused that code , because that’s your actual problem . Sensors take readings from engine exhaust they basicly smell the exhaust . If the fuel is being properly delivered to the engine then the o2 sensor request no changes all sensors are within their set parameters . But if the fuel delivery is not good , the exhaust will not smell right to the o2 sensors .then they will send that info to the ecm , at which time the ecm will start making adjustments in fuel delivery to bring the exhaust back up not its perimeters ! So we only change a sensor if he sensor is out of its perimeters . Which is below or above the own voltage ! But people have been mislead and sensors are flying off the shelf! Because the zone said it was bad lol.you can save thousands by fixing your own vehicle . But people get intimidated , don’t let the car intimidate you. What do you have to lose ? I have had customers bring vehicles in and after a small interrogation , they basicly told me what the problem was but they wasn’t comfortable with their diag skills ! But they was right had they went and just changed the part they diagnosed they could have saved money !now if you wanted to work for a car dealership or somewhere , then you would have to know everything . But not to fix your own car!