Last weekend, one of my car's dashboard warning lights came on. I cursed slightly, because that usually means a fair bit of expense and inconvenience. This proved to be the case this time too - so far its cost $500, the car has been at the menders for 3 days and the light is still on.
One up side is that this has caused me to do some research on the parts of my car that went wrong, and they were two parts that I had no idea even existed.
One is the Exhaust Gas Recirculation Valve. This pumps a small amount of exhaust gas back into the cylinder towards the end of the ignition cycle to cool the reaction and inhibit the oxidation of nitrogen. I knew about NOx pollution from secondary school chemistry but didn't know this was how it was fixed in modern cars.
The other is the carbon canister, which adsorbs vapors from the fuel tank, preventing these vapors from leaking out into the environment while allowing the pressure in the tank to equalize with the external pressure.
Fascinating stuff.