I'm assuming that you are asking about fuel mileage. Reduced fuel mileage is mostly caused by under inflated tires. 32 psi for the Toyota Echo tires is required. Don't buy fuel boosters or fuel cleaners because they don't work.
Most mountains are very close to or are touching clouds, which causes a fog and reduced visibility.
Reduced ozone layer causes skin cancer. It can also cause eye cataract.
Yes, but the mileage for the powertrain warranty is reduced from 100k miles to 60k miles.
A dimmer reduces the voltage to a light so that the current is reduced, which causes the bulb to have a reduced lumen output.
Failure to maintain tune up maintenance.
Running rough? Hard starting? reduced fuel economy? Recommended mileage from owner's manual?
Knocking due to detonation in the cylinders, poor fuel mileage, reduced lifespan.
Diploids
It could be dirty fuel injectors.
causes very poor gas mileage
Poor maintenance, high mileage, contaminated oil (antifreeze),
Running rough? Hard starting? reduced fuel economy? Recommended mileage from owner's manual?