Skip the auto shop - Our mechanics make house calls

Q: How Does Engine Braking Work?

asked by on

How does engine braking work?

Engine braking is the process of using the engine to slow the vehicle down instead of using the vehicle brakes. Engine braking can be used on both gas or diesel engines and is used to slow a vehicle down or control vehicle speed without using the brakes on a steep downhill grade, while also help the brakes from overheating. Engine braking transfers the heat energy to the engine instead of the brakes and releases the heat to the engine cooling system.

The gasoline engine uses engine braking by using the engine’s throttle plates. When you close the throttle plates on the engine, it can no longer pull air in large amounts and the fuel injectors shut off to cut most fuel to the engine. The cutting of fuel and closing of the throttle plates cause the engine to turn by the powertrain instead of the normal engine combustion process of the engine. This in turn will put a drag on the vehicle and slows it down without using the vehicle brakes.

A diesel engine uses different types of engine brakes since it does not have a throttle plate to control how much air goes in the engine and controls how much fuel is injected into the cylinder depending on the need for power. Most smaller vehicles that do not pull heavy weights like a semi-truck and trailer will have a valve that will be in the exhaust outlet of the engine and will shut off the exhaust and fuel of the engine, causing a loss of power and drag on the powertrain versus using the brakes. The other type system, often called a JakeBrake, is a system that will open and close the exhaust valve and fuel injection valve to control the engine backpressure on the powertrain to slow a vehicle, maintain vehicle speed on a downhill incline, or to slow the vehicle to assist the brakes and keep the brakes from overheating.

The overheating of vehicle brakes can lead to dissipation of brake effectiveness, known as brake fading, and can then lead to glazing of the brake pads and brake rotors. Overheating the brakes can also warp the rotors and cause stress cracks in the rotors and pads. When traveling through mountain regions, you might have seen vehicle runoff ramps. These ramps were put there for the big semi trucks that have had brake failure and can no longer stop or slow down their truck. The truck may have had an engine brake system failure and could no longer use the engine to assist the brakes and the brakes got hot to the point of fading. With a heavy load and going downhill, the truck is not be able to control its speed. Therefore, it is important to have a working engine braking system.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Won't move drive reverse

Hi! The screeching sound you're talking about sounds like a worn drive belt and the scraping sound will likely be related to the brakes of the vehicle. I suggest that you have a technician overlook the vehicle and specifically inspect the...

Q: 2006 Audi brake pedal hard replaced booster with no results

To begin with the booster needs a vacuum source. You said you replaced the line, but there is a check valve in the line, it is probably installed at the booster end of the line. It looks like just an...

Q: Leaking inside the car after the rain

A few things can cause water to leak into the car. The most common would be the windshield leaking through, bad door or window seals, an AC evaporator core leaking, or one of the body seams allowing water to pass...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...