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It's possible to test the actual catalytic converter

does anyone know if it’s possible to test the actual catalytic converter, oxygen sensor, or muffler, to know if they’re working properly before replacing them? I have removed the cc, can I take it to a shop or somewhere to get tested, since the car won’t stay on.

That’s normally done with the components in the vehicle as it’s running, with scanner plugged in to monitor those components. So no, there’s no easy way to test these components when they’re out of the vehicle.


If the cat is removed, hold it to a strong light source, like the sun. If you can see any light getting through the cat, this is not our problem. A plugged up cat will not let light through. Similar to an air filter. If it rattles when you shake it, replace it. If you can see light unrestricted, like the grid has big holes in it, replace it. If your CEL is on, and you have codes like P042X, with x being 0 to 9, replace the cat.

I have removed the cc, can I take it to a shop or somewhere to get tested, since the car won’t stay on.

Could you tell us a little more detail here. What do you mean “the car won’t stay on”? With or without the converter? How many miles, what make and model? Any CEL (Check Engine Light), Most important: Why do you think you have a catalytic converter problem rather than something else?

I’ll assume you are talking about a Jeep Liberty, in particular; though the tests of the components you are interested in are, mostly, the same in most other cars and light trucks.
What problems/codes are you having with your vehicle?
Here’s a short primer for checking the parts involved with a trouble code P0420. There is a menu, on that page, for a few other components

You DON'T replace the catalytic converter because the trouble code has the code which contains the name of a component in the code description. 

If you have symptoms, or codes you want to get advice about, let us know.

You DON’T change a part for a trouble code without testing the CIRCUIT the code applies to. The trouble codes are about circuits, NOT the components (directly). Don’t change the catalytic converter because its circuit has set trouble code P0420.

a few weeks ago while driving home on the freeway the CEL came on, flashing. I managed to pull over before total power loss. We had to get the car towed home.
also, while checking the manual for CEL it mentioned that the cc might be failing if the CEL is flashing, which it was

A friend came by with a scanner and this is the code that came up: PO304
I also noted that the spark plug #4 was wet when checked.

I changed the spark plugs and crankshaft sensor.

I was previously able to turn the car on for a bit and noticed it trembled. Now when I try to start it it won’t stay on. I have since removed the cc hoping I can get it tested independently.
Will check the cc with the tips given, thanks.
Although I can’t check if light is shining through 'cause the cc is curved, but I did try
Any other ideas?

Also, if it is the cc, since I live in California, does anyone know where I can get a good price on a compliant cc?

the only ones I can seem to find are “universal,” except for california

my car is a
2002 jeep liberty limited 3.7

I can’t check if light is shining through 'cause the cc is curved
but I did try

i disconnected the battery and erased the code

After a few tries/cranks, the car will start but dies right away
111200 mi
the manual for CEL it mentioned that the cc might be failing if the CEL is flashing, which it was .

P0304 - Cylinder 4 Misfire Detected.

This has NOTHING to do with the Catalytic Converter. Your having other problems, and shooting blind. If the #4 plug was wet with gas, it is more likely the fuel injector is leaking and flooding that cylinder. Even if the coil for that cylinder or spark plug wire was bad, the spark plug shouldn’t be wet. If it was wet with oil, you have bigger problems than even that. You may want to run a compression test and a leak-down test.

Your car tests it continually by comparing the oxygen sensor signal from after the cat converter (the downstream sensor) to the oxygen sensor from before the cat converter (the upstream sensor). If the change in signal does not meet certain parameters, or if one of the signals is out of the normal range, the ECU lights the CEL light. A tech can look at these signals on a scope and diagnose a bad converter. The traces can tell a lot. Once removed from the vehicle a bench test setup would have to be built…no shop is going to have one.

The only way the cat converter can kill the engine is if the ceramic substrate on which the platinum-palladium is deposited were to crumble and plug the outlet, and to be honest that’s quite rare, almost unheard of on newer cars.

I think Bustedknuckles is giving you good advice. I suspect your problems are oethr than the cat converter and you’re shooting blind. You need someone who understands the systems and can help you diagnose the true cause. I applaud your courage in venturing into the foray, but there’s a lot more knowledge you’ll need to get the car fixed.

Sorry, but there’s a whole lot of possibilities here.

You really need to get someone to look at this vehicle who is mechanically inclined. A converter is not just going to all of a sudden plug up and cause the engine to die although it is possible that over time a poorly running engine can contribute to a clogged converter.

You need to start examining spark plugs, wire, coils, etc. first.

It would have been better to have stuck with the original thread you had on this car/problem:

during which the general idea was that going after the cat was barking up the wrong tree.

I’m guessing that you are getting stuck on the cat b/c of what the owner’s manual told you. But if you are really going to try to stick with this yourself you need a repair manual such as a Chilton’s or Haynes - $20 at auto parts stores.

Nice catch cig.