Natural gas smell when holding down brake at light

I have a 2008 Pacifica that was fine for 25000 miles. Then the right front tire blew out and was replaced by the dealer. Since then, I get a very bad natural gas smell inside the car whenever I hold down the brake pedal at a stoplight. The dealer is without a clue, Chrysler tells me its not covered under the extended warranty I purchased, and I’m getting ready to sue somebody. You guys always know the answer, can you help?

You’re getting ready to sue somebody for what? If you ran over a skunk and couldn’t get the smell off the car would you go sue somebody? Do you have some strange idea that purchasing an extended warranty is some right to having a perfect car that is always exactly in order according to your own perceptions? I guess, in other words, what are you talking about?

As for the problem - I can’t think of a single thing about a car that is going to give you a natural gas smell unless you happen to have a car that was converted to run on natural gas. There is especially nothing that has anything to do with a blown and new tire that would smell like natural gas.

Did someone at the dealership drive the car? Did they smell the smell? What did they think about it? Are you sure you know what natural gas smells like (b/c it actually smells like nothing - the odor is added so you can tell if it leaks)? Or are you smelling gasoline fumes? That would make sense.

Or are you smelling something like sulphur (which, I believe, is normally what is added to natural gas to give it its warning odor). If you are smelling sulphur, try a different gas station for a while. Some sulphur goes into some gasoline additives. Different stations may have more or less of certain types. While you’re at it make sure that all recommended maintenance is up to date on the car.

You might want to have someone get under the dash and while holding the brake pedal down, feel the brake light switch above the brake pedal to see if it heats up. Switches encapsulated in plastic can give off all kinds of odors when they start to overheat.


Cigroller is right about the smell. It’s hydrogen sulphide gas out of the cat converter. This gas is used as a warning agent with natural gas and propane, thus the usual mix-up. Cat may be punctured or not working right. I can see why they said a warranty doe not cover smells, but a cat that is not working should be covered. Your smelling it at the stop sign because the cat has heated up and is cooking off the sulphur. Because you are standing still, you get a good dose. Cigroller also right about changing gas stations as another possible.

Yes the dealer drove the car and yes, they too smelled the natural gas odor, from 10 feet away. It doesn’t make any sense. When we bought the warranty the dealer said that it covered "everything "from bumper to bumper. The selling point was that we would have to do no maintenance, only buy fuel.
Someone else thought that it could be the ceramic material in the brake pads. They’d the same smell after a brake job that went away after they replaced the pads.

The dealer said they checked the cat first thing and found no problems with it. The idea of cooking off the sulfer makes sense except that it isn’t a sulfer smell. Turn on the burner on a gas stove, that’s the smell.

You should check for traces of skunk under the car…skunk odor and the additive to natural gas are in the same class of chemicals…mercaptans.

Hydrogen Sulfide doesn’t smell much like t-butyl-mercaptan which is the most common odorant for natural gas. At least not to me. And not to most people I think. However, the way to test would be to start the car in the driveway and let it idle in PARK for ten or twenty minutes. If you get the smell, then suspect the catalytic converter. If you don’t, get in the car, step on the brake and wait. If you then get the smell, suspect an overheating electronic component associated with the brake.

Do an experiment for yourself. The next time you’re in a situation where you would smell it, rather than sitting with your foot on the brake, put the car in park and remove your foot from the brake. Results?

On another occasion, shut down all heat/AC/fan functions being sure that the fresh air intake is closed (set to recirculate). Now see if you smell it.

This might sound odd to you, but check the drive axles, particularly the outer CVs and the inner joint boots well. When the boots break, they throw grease around with can land on hot exhaust pieces, engine/trans, or brakes. The grease in the half-shafts have a particular smell to them that I would say smells like natural gas odorant. I’ve run into that problem before with my brother-in-laws car and it was a broken inner shaft boot. And pretty sure that’ll be covered by your warranty.

We have a 2010 Mazda CX-9 with the exact same issue. It smells just like a natural gas leak which worried us. The dealer checked first for fuel leaks and hasn’t found anything. He mentioned there are a lot of plastic parts that get hot under the hood so I intend to open the hood and sniff around from time to time.