Wow it would be handy to have you around. My car is kind of a lemon. The damage to the body alone means it is totaled. There are cracks in the exhaust manifold, and I don't really have the ability to worry about that. Check engine light has been on for thousands of miles, but every time I go to get it checked they tell me it is something minor that would cost way to much to fix. My main goal is to keep it mechanically running until I pay it off, and potentially a bit longer. Every time I get into it and drive, I praise God it is still working. I want to get a bumper sticker that says "this car runs on the Holy Spirit".
Believe it or not cracks in the manifold will set off the check engine light because anytime the exhaust system has a leak before the O2 sensors, or near them. They will read wrong and the car computer will pick up on that. And that sets off the light.
The computer has a program in it that has the variables that each sensor is supposed to work in. When it happens to fall outside of that, the computer turns on the light. Let's take GMs for a minute. the computer send a 5 volt reference to each sensor except the O2 sensor. The throttle position sensor, which tells the computer how far you are pressing on the gas, works by increasing a voltage signal to the computer as you press on the accelerator. At idle the 5 volts fed to the sensor returns the the computer as around .5 volts (1/2 volt). As you press on the gas the voltage increases by certain increments that the computer is programed to read and know how much fuel to inject. If you floor it you get 4.5 volts. So the operating range is .5 volts to 4.5 volts and the computer knows this. If the sensor goes beyond this range on either end of it it sets that light in the dash.
The map senor is a load sensor. What a load sensor does is tells the computer if you are carrying more weight such as a heavy load, or towing something. The sensor measures the vacuum in the intake where the gas and air get sucked into the cylinder to get burn to create power. If you drive 55mph with no load the vacuum in the intake manifold will be high, If you are driving 55mph and towing something the manifold pressure will be lower which tells the computer to inject a little more gas to compensate for the load.
The Mass air flow sensor measure how much air is flowing into the engine at any given time. How it does this is that there are two or more steal wires that are heated by current. This heat is precise because the current to it is also precise. As the cooler air passes over these heated wires the wires cool. How much they cool determines how much air is coming in through a mathematical equation. And to compensate for changes in outside air temps there is a temperature sensor that measures the air temps before it hits the wires so that the computer will always have a base line temperature to work from.
The oxygen sensor aka O2 sensor is the last check point to see if the computer did the calculations correctly. It has a wire tip that is shielded but has openings that allow the exhaust gasses to flow through it. The platinum tipped wire reacts to any oxygen it come into contact with and it creates a small current. The current created is only in the millivolt range. 500 millivolts is the perfect range.. So the computer will continually try to adjust the other sensors to reach that goal.
The knock sensor detects pre-ingnition (knocking) in the motor and send it's information to the computer and adjustment of the timing of the motor to make it stop.
I hope that helps you in understanding how your car works.