How Hybrids Work
Hybrid-electric vehicles (HEVs) combine the benefits of gasoline engines and electric motors and can be configured to obtain different objectives, such as improved fuel economy, increased power, or additional auxiliary power for electronic devices and power tools.
Some of the advanced technologies typically used by hybrids include:
•Regenerative Braking. The electric motor applies resistance to the drivetrain causing the wheels to slow down. In return, the energy from the wheels turns the motor, which functions as a generator, converting energy normally wasted during coasting and braking into electricity, which is stored in a battery until needed by the electric motor.
•Electric Motor Drive/Assist. The electric motor provides additional power to assist the engine in accelerating, passing, or hill climbing. This allows a smaller, more efficient engine to be used. In some vehicles, the motor alone provides power for low-speed driving conditions where internal combustion engines are least efficient.
•Automatic Start/Shutoff. Automatically shuts off the engine when the vehicle comes to a stop and restarts it when the accelerator is pressed. This prevents wasted energy from idling.
Some of the advanced technologies typically used by hybrids include:
•Regenerative Braking. The electric motor applies resistance to the drivetrain causing the wheels to slow down. In return, the energy from the wheels turns the motor, which functions as a generator, converting energy normally wasted during coasting and braking into electricity, which is stored in a battery until needed by the electric motor.
•Electric Motor Drive/Assist. The electric motor provides additional power to assist the engine in accelerating, passing, or hill climbing. This allows a smaller, more efficient engine to be used. In some vehicles, the motor alone provides power for low-speed driving conditions where internal combustion engines are least efficient.
•Automatic Start/Shutoff. Automatically shuts off the engine when the vehicle comes to a stop and restarts it when the accelerator is pressed. This prevents wasted energy from idling.
Fuel Economy Estimates
How are fuel economy ratings determined?
EPA estimates are based on laboratory tests conducted by manufacturers according to federal regulations. EPA re-tests about 10% of vehicle models to confirm manufacturer's results. For more detailed information, visit our page on How Vehicles Are Tested.
Why does my fuel economy differ from EPA estimates?
No test can accurately predict fuel economy for all drivers and all driving conditions. Driver behavior, driving conditions, vehicle maintenance, fuel characteristics, weather, and other factors can all affect fuel economy significantly as explained here.
What should I do if my fuel economy is excessively low?
If your fuel economy is excessively low, your vehicle may need to be serviced or repaired. You may want to contact your dealer or a reputable repair facility to check your vehicle. The following are some of the diagnostic checks a mechanic will typically conduct for poor fuel economy:
•Perform "On-Board Diagnostic System Check" for diagnostic trouble codes (sensors or actuators which may be malfunctioning)
•Check for dragging brakes
•Check transmission shift patterns for slipping, use of all gears, lock-up operation
•Check ignition timing
•Check owner's driving habits including A/C usage, hard accelerations, carrying heavy loads
•Check emission control system
•Check vacuum hoses for leaks, kinks, proper routing
•Check tire pressure
•Check fuel type, quality, and alcohol content
•Check fuel pressure and fuel system for leaks
•Check air cleaner element
•Check coolant level
•Check ignition system for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits, cracking or improperly connected ignition wires
•Check for proper calibration of speedometer
•In extreme cases, there may be engine problems such as poor compression or faulty fuel injectors
Why don't you have ratings for large vans, pickup trucks and SUVs?
Vans, pickup trucks, and sport utility vehicles (SUVs) weighing more than 8,500 pounds gross vehicle weight are classified as heavy-duty vehicles. Fuel economy regulations do not apply to these vehicles, so they are not tested.
Where can I find more information about Corporate Average Fuel Economy (CAFE)?
First enacted by Congress in 1975, the purpose of CAFE is to reduce energy consumption by increasing the fuel economy of cars and light trucks. Information on CAFE is available from the National Highway Traffic Safety Administration.
Do EPA fuel economy estimates account for the use of ethanol blends that are common today?
No. The EPA fuel economy tests use 100 percent gasoline, and no adjustments are made to account for ethanol. Most conventional vehicles using E10 (10 percent ethanol) will experience a 3 to 4 percent reduction in fuel economy.
Why don't EPA fuel economy tests use ethanol-blended gasoline now that most gasoline contains ethanol?
EPA fuel economy tests are conducted according to Federal testing regulations which require 100 percent gasoline. These regulations could be changed, but changing them would be somewhat problematic. While it is common for gasoline pumps to allow for up to 10 percent ethanol, the actual amount of ethanol blended into the gasoline varies greatly, and fuel blending requirements vary by state. Changing the test methods would also make it difficult to compare vehicles tested with ethanol blends with those tested with straight gasoline. So, without a national standard for blended regular gasoline and a Federal mandate to change the test fuel used, the EPA will not change the test fuel.
EPA estimates are based on laboratory tests conducted by manufacturers according to federal regulations. EPA re-tests about 10% of vehicle models to confirm manufacturer's results. For more detailed information, visit our page on How Vehicles Are Tested.
Why does my fuel economy differ from EPA estimates?
No test can accurately predict fuel economy for all drivers and all driving conditions. Driver behavior, driving conditions, vehicle maintenance, fuel characteristics, weather, and other factors can all affect fuel economy significantly as explained here.
What should I do if my fuel economy is excessively low?
If your fuel economy is excessively low, your vehicle may need to be serviced or repaired. You may want to contact your dealer or a reputable repair facility to check your vehicle. The following are some of the diagnostic checks a mechanic will typically conduct for poor fuel economy:
•Perform "On-Board Diagnostic System Check" for diagnostic trouble codes (sensors or actuators which may be malfunctioning)
•Check for dragging brakes
•Check transmission shift patterns for slipping, use of all gears, lock-up operation
•Check ignition timing
•Check owner's driving habits including A/C usage, hard accelerations, carrying heavy loads
•Check emission control system
•Check vacuum hoses for leaks, kinks, proper routing
•Check tire pressure
•Check fuel type, quality, and alcohol content
•Check fuel pressure and fuel system for leaks
•Check air cleaner element
•Check coolant level
•Check ignition system for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits, cracking or improperly connected ignition wires
•Check for proper calibration of speedometer
•In extreme cases, there may be engine problems such as poor compression or faulty fuel injectors
Why don't you have ratings for large vans, pickup trucks and SUVs?
Vans, pickup trucks, and sport utility vehicles (SUVs) weighing more than 8,500 pounds gross vehicle weight are classified as heavy-duty vehicles. Fuel economy regulations do not apply to these vehicles, so they are not tested.
Where can I find more information about Corporate Average Fuel Economy (CAFE)?
First enacted by Congress in 1975, the purpose of CAFE is to reduce energy consumption by increasing the fuel economy of cars and light trucks. Information on CAFE is available from the National Highway Traffic Safety Administration.
Do EPA fuel economy estimates account for the use of ethanol blends that are common today?
No. The EPA fuel economy tests use 100 percent gasoline, and no adjustments are made to account for ethanol. Most conventional vehicles using E10 (10 percent ethanol) will experience a 3 to 4 percent reduction in fuel economy.
Why don't EPA fuel economy tests use ethanol-blended gasoline now that most gasoline contains ethanol?
EPA fuel economy tests are conducted according to Federal testing regulations which require 100 percent gasoline. These regulations could be changed, but changing them would be somewhat problematic. While it is common for gasoline pumps to allow for up to 10 percent ethanol, the actual amount of ethanol blended into the gasoline varies greatly, and fuel blending requirements vary by state. Changing the test methods would also make it difficult to compare vehicles tested with ethanol blends with those tested with straight gasoline. So, without a national standard for blended regular gasoline and a Federal mandate to change the test fuel used, the EPA will not change the test fuel.
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