How can I diagnose for a bad catalytic converter?

I want to try to be sure my cat(s) is bad before I bring it in to the dealer for the extended cat. warranty, since they say they will do whatever work they want and charge me for it. Can someone tell me the dealer service procedure how it will work? I couldn’t get a straight answer out of the guy on the phone. Do they test the cat, or do they replace a bunch of parts before they blame the cat or what?

 

You can visit gearchatter.com and look up P0420/P0430 for your year. I know a couple people that got their's replaced free after being told over the phone there was a diagnostic charge, could be an 02 and not covered, could be an exhaust leak, etc. etc. etc. Leave the code(s) alone if the SES is on, and tell them to call you for authorization for anything other than replacing the cat. Are you throwing the above codes?

 

Is your SES light on? If so go to Autozone and they will scan it for free. It will tell you which one is no good. Bank 1 is the driver side, Bank 2 is the passenger.

Or just buy some LTs and loose the cats all together. You can sell your stock cats for up wards of a hundred bucks.

 

SES light is not on. The reason I think cats is, I thought I had a bad fuel filter it feels like, but new filter and it's still the same. So I'm thinking it's the cat issue. Know if the cat issue normally trips a code? I figure since no code, extra back-pressure should be about the only thing possible to bog me down without throwing a code...any thoughts?

 

Bad cat(s) will throw codes - don't look for the free replacement if you bring it in.

 

are you sure? from experience or guessing? what codes?

 

My guess is the dealer will rape you, either from them having more knowledge than you, or not having enough themselves. If it's not throwing a code how do you know it's the cat? Just a guess?

Dealers will try to screw you over anyway they can and make it seem like your getting a good deal. My dad's been a mechanic at a dealership for 30 years.

 

If your cat is bad it will set off your SES light and throw a code.

 

if you jave access to a advanced scan tool, with the car running, check to see what the o2 sensor after the cat (either bank 1 sensor 2 or bank 2 sensor 2) is doing. if it is not a constant voltage then the cat is probably bad

 

Both my friends had P0420 for bank 1 when they got the drivers side replaced free - that's why I suggested looking up P0420/P0430.

 

I threw a bad cat code at one point 2 months ago... for some reason or other the code went away and never came back... but the car still feels sluggish as hell...

that being the case, I wouldn't jump to say that a bad cat will ALWAYS necasarilly throw a code...

 

Does yours always feel sluggish, or just when you give it too much gas? Mine feels completely normal until I give it too much gas, then it gets really choppy and never recovers until I let off, then just drives normal again as long as I don't gas it too much...all without setting off any codes.

Anyway, I used a scan tool today, and got no codes.

I also made an appt at the dealer before that, but I'm going to cancel it until I think about it more at least. I so don't trust dealers...83 bucks an hour he said...yikes lol.

So talking with the guy at advance auto parts today, thinking maybe it's an in-tank issue, either pump, or clogged screen or something. How tough is it to drop the tank and pull the fuel pump to inspect? I'm thinking of just bringing it to a mechanic and having him do that to start with. What do you guys think? Is there a strainer screen in there you can clean out?

 

As a pontiac dealer tech i can tell you that is not true. Just the other day a firebird (v6 but same exhaust essentially) came in complaining that his car lost power on the highway and died. He had a misfire condition previously that was repaired. How ever the cat was damaged but the people who fixed the misfire didn't catch it. so i test drive it and sure enough when you accelerate the car will just hit a wall at about 3000 rpms. Also the SES never came on at all while this was happening. so i drop the exhaust to check the muffler, then drop the y-pipe to confirm that the cat was clogging up.


CLIFF NOTES: Bad cats don't always throw codes.

 

So if I drop the y-pipe I can tell if the cats are bad? How, does the inside appear obviously damaged or what?

 

For the most part yes... It drives pretty normal until i give it gas, then it's almost as if it takes a second or two for the engine to realize I hit the throttle, then it sluggishly tries to accelerate... I'm getting LT's and an ORY anyday now, so I'm hoping when I get those it'll solve my problem...

 

Bad cats will throw codes for different reasons, if the OP looked up P0420/P0430 they're listed in the diagnostics. Alternative is to just bring it to the dealer and let them figure it out, and charge their diagnostic fee before even working on the car. Since no codes are thrown the bogging issue could be a lot of different things, not necessarily the cats.

 

Should my belt tensioner jiggle slightly while idling? Should I be able to push it towards slack while putting medium light pressure with my hand? Maybe 40 lbs of force on the pulley to untension the belt.

Also, could a slipping belt cause me to lose alot of power but still run otherwise normal? It looks like my belt has been doing burnouts on my waterpump pulley(the big one on top?), if it slipped on the crank pulley too, maybe I would lose voltage and bog?

I'm not sure, but I know I'll get a new belt. A tensioner too if you guys think mine sounds weak...by the way, all the other cars we tried the tensioners seemed stiffer, but wanted some opinions.

 

About dropping the y-pipe to check the cats, what do you do, look in there for damage...how do you know they are toast by looking inside them?