Q: How Does Engine Braking Work?

asked by on December 01, 2015

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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

What others are asking

squeal sound from rear passenger wheel when driving bumpy roads

The noise is probably brake or wheel bearing related. If brake related, it might be due to the brake pad wear indicator contacting the rotors. If you desire that this problem be diagnosed by a certified Mechanic, dispatched by YourMechanic...

Engine turns over good but won't start what might be the problem? It misfired one time and hasn't started since.

Your engine requires spark, air, and fuel to start and run properly. Air is almost always present so that leaves spark and fuel. Depending on the vehicle, if a crankshaft sensor is faulty, the engine control unit may not receive...

Engine running rough

Quite a few things can account for an engine running rough. It could be just one cylinder misfiring, or multiple. If the Check Engine Light is on, the computer has detected a problem and the code(s) will help narrow it...

I have oil and water mixing in the engin but there is no oil in on the plugs.

No. There is only 1 common possibility for this engine to get water into the oil, and that is a blown head gasket. This often, but not always, follows an overheating event, and some times also occurs with vehicle mileage...

Service "A" with low tire pressure reading needing scheduled maintenance.

Service A is supposed to be performed after the first year/10,000 miles of ownership, then every 2 years/20,000 miles going forward. This service includes: Oil and filter change Resetting of the maintenance reminder Tire condition/pressure check (this will...

Brakes issue

The squealing might be due to the brake bad wear indicators contacting the rotors. That noise alerts you to the need to install new brake pads. Regarding the cost, there are a few variables affecting the cost. If you are...

Is the wheel bearing and rotor made all together? How do I get the rotor off?

Hello, thank you for writing in. False, the rotor and the wheel bearing are two separate components. The rotor just becomes incredibly hot and dirty fusing it into place. If you have a lot of dust, snow, or rain in...

Speed vs. Torque

If you compare the concept to some small remote control cars and trucks out there, they have a two speed rear ends to have great low speed torque and use shift gears to have great high speeds. When it comes...

What is the anti-lock brake self-test?

The anti-lock braking system (ABS) on your car is designed to conduct a self-test every time you crank the engine. During the test, the ABS light on the dash will turn on, and then should go out after a few...

Related articles

Top 10 Ways to Extend the Life of Your Car
Every driver wants a car that lasts a long time. Make your car last longer by checking your motor oil, parking in the shade, and keeping it clean.
Does Running My AC in the Summer Keep My Engine Cooler?
When When you engage your air conditioning in your car, it is usually summertime and hot outside. Air conditioning serves to remove heat from the inside of your vehicle by circulating a refrigerant through the evaporator core in your dashboard,...
Is it Safe to Drive With the ABS Light On?
The ABS warning light means the anti-lock braking system isn’t working properly, and may not work if you need to stop your car quickly.