Skip the auto shop - Our mechanics make house calls

Q: Is there a smell which develops in a car when the catalytic converter starts to go bad?

asked by on

About one week ago, a strong unpleasant odor developed in my car. It just started one day; nothing I can think of was the cause. I had my local tire shop put the car up on their rack to inspect the underside chassis for maybe a small animal nest. Found nothing inside or out. A gas station attendant I use on a regular basis thought the smell (rotten eggs) might be the start of trouble with the catalytic converter. Any truth to that claim?

My car has 147500 miles.
My car has an automatic transmission.

A: Hi there. If there is a rotten egg or sulfu...

Hi there. If there is a rotten egg or sulfur type of smell then most of the time this is caused by a failure in the catalytic converter. When these fail and become too hot they will smell like this. It needs to be tested with a temperature gun or with a back pressure tester. Both of these will help to identify this as the problem. A cylinder misfire will also cause this to occur. If you want to have this exhaust smell diagnosed, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose and repair this.

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: Hi - Knocking noise

Hello. If there is a knocking noise then it may have some bad fuel or it may be another failure like an internal engine problem or a bad sensor. I usually start the diagnostic process by scanning the computer for...

Q: Rough idling during cold starts

The vehicle will have to have the throttle body and idle air control valve checked to see if it needs to be cleaned. Also, the engine will need to be checked for any vacuum leaks when the engine is cold....

Q: What is the best fix for a catalyst system efficiency below threshold (bank 2)

Trouble code P0430 is for a catalyst on the drivers side. The sensor after the converter may be bad and not responsive enough or the catalyst itself may be bad. The catalyst should be replaced if the converter rattles, there...

Related articles

What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
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...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.