It’s enough to gag anybody when you start your car and smell a horrible, rotten stench. If it smells like sulfur or rotten eggs, something is wrong.
Here we discuss the possible causes of a car smelling like rotten eggs and how best to eliminate the smell so it doesn’t hang around and make you and your passengers think fresh air is a luxury.
Why Does My Car Smell Like Rotten Eggs?
There are a few reasons your car may be starting to smell like rotten eggs, and before you contact a mechanic to have them diagnose the culprit, getting some understanding of the problem may be helpful.
Whether you’re going to resolve it on your own or just want to know your mechanic isn’t taking advantage of you, here are five different reasons for a rotten egg smell in your car.
#1. Bad Catalytic Converter.
This is the most common reason for a rotten egg smell in your vehicle. When your vehicle is in good working order, your catalytic converter takes toxic chemicals and makes them harmless H2O compounds, aka water/steam.
However, over time, these harmful chemicals and gasoline can clog up parts of the catalytic converter, and when that happens, it can no longer do its job.
With a plugged catalytic converter, instead of changing to water or steam, the hydrogen sulfide changes to sulfur dioxide, which gives you the rotten egg smell.
#2. Bad Fuel Pressure Sensor.
One of the most common times there is a rotten egg smell in your vehicle is when a bad fuel pressure sensor is dumping too much fuel into the system, which is clogging up your catalytic converter because it can’t process that much at once.
This is particularly true if your catalytic converter is failing sooner than you would expect it to fail, which is about ten years or 200,000 miles.
Keep in mind, even with a bad fuel pressure sensor and a rotten egg smell, you will still need to swap out the catalytic converter too.
This isn’t an either/or option, it’s only a matter of whether you need to swap out both components so you don’t prematurely wear out your vehicle’s new catalytic converter.
#3. Old Transmission Fluid.
If you have an older car (a manual), you probably have to change your transmission fluid from time to time.
Your owner’s manual lays out the exact service intervals, but if you are neglecting to change it when you should, it can cause seals to wear down and start leaking transmission fluid where it doesn’t belong.
When that does happen, this can create a multitude of smells, but is often described as rotten eggs or sour milk.
If this is happening to your vehicle, you need to change the transmission fluid, but you will most likely have to replace a few gaskets or seals too.
#4. A Dead Animal.
While everything we have touched on is mechanical issues, there are a few other options.
One that occurs more than you could believe is a dead animal (usually a mouse or rat) in your engine bay, or exhaust system, or ventilation system, or car interior…
When the weather gets cold, animals look for a warm place to sleep, and your engine bay or exhaust system is an appealing spot. The downside is, when you start your car, you may end up killing them, and their body starts to decompose.
As you can imagine, this is not a good smell, and could be the reason you have a foul odor following your car around.
#5. Forgotten/Hidden Groceries.
Sometimes a rotten egg smell is just that, a rotten egg. While this could be the least likely possibility, sometimes, unfortunately, groceries slip through your car and hide under various seats.
Or maybe you’re going through a nasty breakup and your ex cracked an egg in your car without you knowing.
Either way, sometimes if you smell rotten eggs in your car, it’s because you have a rotten egg, or spoiled milk, broccoli, or some other rotten groceries in there!
Is My Car Still Drivable?
You may think driving around with a rotten egg smell isn’t a big deal, especially since it likely involves an emissions component but we don’t recommend it for any amount of time because of the risk.
Next, if the catalytic converter is clogged, it can overheat, and if it overheats enough, it can catch fire. Obviously, this worst-case scenario is one reason you don’t want to ignore a rotten egg smell!
How Can I Fix the Rotten Egg Smell?
Ok, you tried to ignore the rotten egg smell in your car, but now that it’s there, let’s look at what you need to do to take care of it.
You can simply take it to a mechanic, and you could even do that first. However, regardless of whether you decide to have it fixed or not, we highly recommend doing the following steps so you can be informed of what is going on, and the mechanic will not try and take advantage of you in any way to possibly charge you more than it costs.
Step 1: Scan with a Scanner for Trouble Codes.
First, there is a good chance you will have a check engine light at this point, too, and the first thing you want to see is what the code is telling you.
You can either get your own top-quality automotive scan tool to do this, or you can take it to a local parts store like AutoZone, which will read the code for you for no charge.
Even if you don’t have a check engine light, we highly recommend doing this on the vehicle to make sure there is no code and a faulty check engine light.
#2. Check Transmission Fluid.
Next, check the transmission fluid service interval for your vehicle, and compare it to the last time someone changed the oil. If there is a major discrepancy here, then there is a good chance it is transmission fluid-related.
If you have a low amount of fluid, then you will have to check through a ton of different parts to see if it is leaking anywhere, then fix the leak and change the fluid.
#3. Search Your Vehicle.
However, if there is no code and the transmission fluid is not old, then it may be time to start searching your vehicle. It is possible that the converter is going out and there is no check engine light, but that is a little odd.
Just do yourself a favor and go through everything to rule out hidden groceries, a prank, or a dead animal somewhere.
#4. Check Fuel Pressure Sensor.
The next recommendation is to look at the output specs on the fuel pressure sensor, but you will need an automotive scan tool for this. It is also unlikely that the fuel pressure sensor is failing with no engine code.
After checking all these things, it is a relatively safe assumption to think that the odor is coming from a faulty catalytic converter. Simply replace the converter to eliminate the odor!
Will The Odor Go Away By Itself?
One thing is for sure: if you have a rotten egg smell in your car, it is not going to go away by itself. In fact, if you do not troubleshoot the issue and tackle it, it is only going to get worse.
It does not matter if it is groceries, you missed, or a faulty converter; the problem is only going to get worse until you remove the cause!
If you are unable to do the work yourself, we would recommend taking your vehicle to a mechanic sooner rather than later, so they can provide you with an estimate and fix what is going on.