No Catalytic Converter on 04 Honda Pilot

So my 2004 Honda Pilot doesn’t have a catalytic converter on it because I took it to a friend and he cut it off and I guess just basically straight piped it. He said it was bad. Ok, I’m no mechanic so I didn’t think much about it until I started having problems. I have bought a new one and o2 sensors to put back on it but for now my problem is at start up it idles rough. After starting it, as I first start driving it, it will act like it’s about to stall out but doesn’t so I press the gas enough to get it to go then it’s fine while driving. Then It started running hot when I’d idle like in the school pick up line or long red lights. I changed the thermostat and it was fine for a few days then started running hot again when idle. I had one guy tell me it was the Idle Control Valve which got cleaned out but still idles rough. Anyone know if all this could be from not having the cat on it? Also has an exhaust leak from the guy not welding the pipes on properly. Need help fast!


Anyone who cuts the cat out of your vehicle is no friend.


Removing a catalytic converter and replacing it with a any kind of pipe is a Federal and State offense. Which can incur sever fines.

Third. And most important is,

Any shop who see’s that there is no longer catalytic converter in the vehicle may refuse to service the vehicle because the vehicle is no longer street legal. And a shop isn’t going touch a vehicle that isn’t street legal so it can be put back on the street.

And Finally.

Removing the cat removes some of the exhaust back-pressure. And this can effect how the engine runs.

Best you can do is, bring the vehicle in and have a new cat installed. A shop will do that because you’re now making the vehicle street legal.

I wonder how much that so-called friend got for your cat when they recycled it?


From what I’ve been told in South Carolina there’s no emission law saying you have to have a catalytic converter. But I’d feel better once it gets put on. The friend told me it was clogged and would run better with it off but the research I’ve come across says that vehicles a certain year and newer won’t run properly without one.

Federal law trumps state law, always. And the law preventing removal is federal. Just because you have no inspection doesn’t mean you can remove the cat.

The exhaust leak needs to be fixed, a new cat needs to be installed and then you can read the engine codes and see what is actually wrong with this xxx,xxx (you don’t say) mile car.

The state of South Carolina has no say in the matter.

It’s a federal law.


If South Carolina is still part of the United States then there is a federal law that requires your car to have a catalyst. Getting one installed is the first step in getting the car fixed right.

Sounds like you may have more than one issue with the car or possibly some engine repair looming ahead.

There is a front cat and a rear cat. They look a lot alike. Both are vertical. They dump into a y pipe under the motor. Don’t know what your friend cut off. Since you have 2 cats.

To make sure I understand, you still have not put on the cat-conv? Is the check engine light on? If so, have someone read the trouble codes and then look them up online.

Pulling the cat-conv and/or sensors should have turned on the Check Engine. Both sensors are usually required for proper operation. When one or the other fails (or is missing) it can cause the engine to run too rich or lean. My front O2 sensor was replaced w/ a defective one. After 4 months, the car had problems until it warmed up.

Don’t worry about the naysayers on here, but they are right about one thing… your friend blew this one. I hope an exhaust place can fix the problem w/o purchasing the whole exhaust. Some cars reject aftermarket cat-convs.

I wonder if this car has several issues that are not related to the converter. It is 16 years old with an unspecified number of miles.

A rough idle could be due to low compression, ignition miss, vacuum leak, and so on. Overheating could be due to a flaky radiator cooling fan, fan relay, or thermostat to name a few.

I am curious as to why you let this “friend” cut the converter off. Someone give you a diagnosis of a bad cat and he volunteered to rid the car of that “unnecessary garbage” or something???

Check engine light is on. Codes read running too lean which has to do with the o2 sensors and Cat. It’s in the shop now.

I’ve also been told (without them actually looking under the hood) I may have a head gasket problem.

Yes, probably the missing after-cat O2 sensor. As I recall, if
too much carbon gets past the cat-conv, the computer leans the

Is the cooling system full?

If the engine is overheating and misfiring during start up you should focus on that, if your engine is damaged and needs to have the head gaskets/cylinder heads replaced the catalytic converter can be replaced during that repair but this type of engine repair wire be very expensive.