One of these might be a good investment for DIY and you will have a definate idea.

https://www.ebay.com.au/itm/13517399...Bk9SR6qxhcuEZg
It looks like it has the most common size thread 18X1.5mm but if you buy one check first.
You can buy cheapies but.

 

Or for less money you can scan the ECU and look at the CAT operating temperature at idle .

I think that is an expensive tool for a DIY one time use, unless he is like you and I that likes to collect tools ?

 

You can get them for abt $20 but you get what you pay for. Not all cars have a pid for cat temp.

 

no they don’t but then every DIY should have at least a hand held digital laser temperature gun for about 18 usd . That way it is more useful for a multitude of testing not just automotive .

I have about 4 all the same model. 1 in the house, one in my to go small travel tool bag, one as a back up and one in the tools in the garage. I probably use one of them at least every other day .

Oh I forgot I have a very expensive one that stays in the house with my high end Dignostic equipment because it was almost 250 usd it can measure reflective material temperatures .

 

That's OK if you want to read cat in/out for efficiency but in the case of being blocked the intake vacuum is a good test but like most things requires a better understanding of what to look for particularly with a scantool.

 

Because there's 3 cats on the car I was trying to see if I could narrow it down
But your right could be worn rings bummer it's done 300k kms

 

For an Aussie car that's a huge overkill for 2002.

 

One of those gauges is probably the best way. You can get them cheap on eBay. I'd start at the last one and work forward till you find the blockage. I have never attempted to clean a CAT but I believe ultrasonic can do it. The do the Diesel DPF's that way.

 

Another sign of a blocked exhaust is when opening the throttle the intake makes a loud throaty roar noise and the engine won't rev up.

 

Um…. You only need to measure the case temperature which can indicate a failing , a failed or blockage to a CAT . We should
be trying to make this easy for a DIY. You and I have all the tools while a DIY does not. So a better idea is a tool if needed to be purchase have more then one use.Better investment ,home, garden, hobby and auto servicing . lol

Not sure why I failed to mention the thermal gun earlier, but I over think at times service challenges.