Symptoms of a Failing Exhaust Resonator

Mia Bevacqua
July 13, 2018

Signs of a failing exhaust resonator

A faulty exhaust resonator can do more than just be noisy. If left unchecked, it could keep your car from starting, or even endanger your health. Here are some symptoms of a bad one.

1. Engine performance and fuel economy suffer: To provide adequate performance, an engine must be able to breathe easily. A collapsed resonator chokes the engine, resulting in a lack of power and reduced fuel economy.

2. The check engine light is on: Occasionally, a collapsed resonator can affect performance to the point that the check engine light comes on.

3. The engine stalls or won’t start: In extreme cases, a collapsed resonator may create enough back-pressure that the engine stalls or won’t start. The oxygen sensors will read lean when there is excessive back-pressure.

4. Excessive noise: A damaged or failed resonator can result in unwanted noise coming from the vehicle’s exhaust. Typically, the sound is described as a high-frequency buzzing.

5. Unusual smell: A leaking resonator can allow noxious fumes to escape from the vehicle’s exhaust. Not only can this cause an unpleasant odor, it can be a health hazard.

The entire exhaust system is a torture chamber for steel. Mufflers and resonators rust from the outside in, due to rainwater, snow and road salt, while simultaneously rusting from the inside out because of corrosive exhaust byproducts and extreme temperature changes. 

Cars from the 1960s and ’70s used steel for the exhaust. The steel quickly rusted out and was a regular auto repair in those days. Today, federal emissions regulations require that emission components are built to last. This forces manufacturers to use expensive nickel-steel alloys that last much longer.

But they’re still not lifetime components. Inspecting the rubber exhaust hangers and motor mounts can go a long way in reducing exhaust component failures. 

» LEARN MORE: Get an estimate for your car repair

How to fix the problem

Before spending time and money to replace the resonator, a thorough diagnosis should be performed. A professional will inspect the entire exhaust system, checking for leaks and damage.

A faulty resonator should be replaced a soon as possible. In many cases, the job involves cutting the old unit out and welding the new one in. This is a difficult task that should be performed by a professional equipped with the right tools.

Get it diagnosed by a professional

What a resonator does

If you're not sure of the difference between an exhaust resonator and a muffler, you're not alone. Although these components are similar, they serve two distinct purposes.

The resonator cancels out specific sound frequencies created by the engine, while the muffler lowers overall engine noise. 

The resonator is a type of echo chamber designed to create a pleasing exhaust note. It alters — but does not reduce — the noise coming out of the engine. Sound waves bounce around, or resonate, inside until the undesirable ones cancel each other out. This process preconditions the tone of the exhaust before it enters the muffler. 

Next, the sound waves enter the muffler for noise reduction. Engine noise is lowered as exhaust gases pass through or around a series of tubes and baffles. For further reduction, many mufflers also contain sound-deadening materials, such as fiberglass. Every time the exhaust gasses make a turn or directional change inside the muffler, tailpipe noise is dramatically reduced.

Both components are part of the exhaust system underneath the vehicle. The resonator is sometimes located before the muffler, but on most modern cars, the two are integrated into one assembly. Because of its location, the resonator is sometimes called a “pre-muffler.”

Mia Bevacqua

About the Author

Mia Bevacqua is an automotive expert with ASE Master, L1, L2 and L3 Advanced Level Specialist certification. With 13-plus years of experience in the field, she applies her skills toward writing, consulting and automotive software engineering.

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