Chapter 4 — Your Driving 65 The air pressure of tires must be checked at least once each month. For safe  driving and fuel economy, tires should have the right amount of air. Follow the  manufacturer’s recommendation. The best time to check air pressure is when  the tires are cool. If you do not have an air pressure gauge, you can take your  vehicle to a nearby service station or auto center to have it checked. Every motor vehicle must have a muffler that is in good working order. The  muffler filters smoke and excessive noise. One function of the exhaust system is  to take harmful fumes from the engine to the rear of the vehicle to be released.  Check your exhaust system often to be sure it is not leaking. A leak in the  exhaust system can allow poisonous carbon monoxide gas to enter the passenger  compartment of the vehicle. Carbon monoxide poisoning often can be fatal,  and even small amounts can cause you to become sleepy or unconscious and  lose control of the vehicle. For this reason, it is suggested that you keep a  window open about one inch while traveling. If a vehicle sways freely, leans heavily to one side during a turn or seems to  bounce continuously, there may be a problem with the suspension system.  Have a mechanic inspect the suspension system, including shock absorbers, and  immediately correct any defects. A faulty suspension system can cause you to  lose control of the vehicle. Vehicles are equipped with an emergency warning device that flashes all four  turn signal lights. These flashers can be used as a warning by any vehicle to  signal other drivers of a possible danger or that a vehicle is stopped or disabled. Driving green means adopting a few simple, inexpensive driving habits to  decrease the amount of fuel you use and put more money in your pocket.  • Every five miles over 60 mph can cost you up to an additional 30 cents a gallon.  • Check tire pressure once a month and keep tires properly inflated. • When you carry extra weight, your vehicle must work harder.  •   Every licensed motor vehicle must be equipped with a horn in good  working order. • The horn must be loud enough to be heard for at least 200 feet, and it  must not make any unreasonably loud or harsh sound. • If the horn fails, have it repaired immediately. • The horn must be used as a reasonable warning device. You should not use  the horn unnecessarily or unreasonably. Horns and Sirens Only law enforcement and emergency vehicles may have emergency lights or sirens. Muffler and Exhaust System Suspension System Emergency Warning Flashers Drive Green 