[ImperialCrown]

I usually erase the code the first time it happens, just to be sure that it isn't a fluke. A battery disconnect, pause and reconnect should erase the fault code. On the JX, the battery is hard to access, so I just unplug both PCM connectors or unscrew both of the underhood neg battery jump start nuts. If you power down the whole car, you will need to reset the clock and possibly stations if it isn't a Chrysler radio.
Sad to say, it is usually a real cat failure and it may take about 3 days for it to come back depending upon your driving habits. The PCM compares the upstream and downstream O2 signals to determine cat health, so the O2 sensors and EGR get tested first.
An aftermarket 'direct-fit' catalytic converter is the best way to go if you need one (except CA). No cutting, bending or welding, it goes in like OEM. If the rest of the exhaust system is weak or rusted you may have to address that now as well.

 

[marcpilot1]

wow, that sounds exactly like what im going to do. like right now. I will disconnect the negative after accessing the battery from behind the drivers wheel? How long does negative need to stay off before reconnecting? And when i access the the bottom of my car and look for rust or holes or damage, if I find any, could that be the reason for code and not necessarily cat gone bad? And the sensors, my obd2 is pretty top of line, actron cp9580. like could I hook it up while driving or something to get info from one of the many graphs on it? They look somewhat like an EKG. Can it tell me info to let me know if sensor or sensors are poss bad? I mean does the obd have that technology? Ok, pull negative, rehook it back up. Wait couple days to see if cel comes back on. Not sure how long to leave negative off before reconnecting.But, If cel comes back and its p0420, start with.....what of all things would you do do next?

I forgot you said to unhook the 2 jumpstarts. sorry. I'll just do that. Do you know where the pcm connectors are on my car?

 

[ImperialCrown]

A minute of power-down should be enough to erase the code. You can disconnect the battery under the hood at the jumper terminal instead of pulling the LF wheel and splash shield.
It is much easier that way, but on the other hand getting at the battery gives you the opportunity to inspect and clean your side post battery terminals. Use safe jacking and support practice. Take them right off the battery and wire brush them for good contact. That operation alone should be plenty of time for the PCM to reset its diagnostic memory.
Many times the out-of-sight, out-of-mind battery is trouble when it is most inconvenient, so occasional inspection and cleaning is a good service.
If you don't hear a loud exhaust, it is probably intact and free from holes. The stainless steel is wonderful for lasting many years, but 14 years would be a long time for an original system. During the negative pressure pulse of the exhaust stream, it can draw air (oxygen) in through a hole and skew the true oxygen content of the exhaust. This could cause driveability concerns (lean) and set false codes.
The upstream O2 sensor switches about twice the rate of the downstream O2 sensor after warming up. This is what the PCM uses to determine catalyst performance. A warm O2 on a running engine should never sit still, stay at 0 or peg + or -.

 

[marcpilot1]

Well, youre exactly right. I unhooked the jumper posts for 10 mins and "service engine soon" or whatever it says on the cel is Gone! I know, it'll prob be back in 2 days. So, when it comes back do I then check upper and lower sensors next? Btw, u were right about the stainless. I got under and looked from near the front to the back and no rust that I could see. It looked pretty good actually. If sensors are next do you know where the front or upper one is and how to check it? (remember, i do have the Actron cp9580) And the same for the back one or lower? I did see a wire going into a sensor looking device near the front of the exhaust. Didnt see anything near the back of the exhaust though. But the one near front seemed to be between cat and motor. I took a couple pics while down there but i assume nobody can look at em or needs to. Maybe. Thanks for everything so far! A lot. Marcpilot1- Oh yea, dont have loud exhaust at all. Its quiet and smooth as can be.And I think I get it. The downstream and the upstream sensors might be right by each other. or maybe even one piece. And if negative pressure is detected from the downstream it could set the false code. Ohhhhh. Ok, I think. I need to find those 2 sensors. Then check em somehow. I get it! I think. Thxxxx-

 

[ImperialCrown]

If you get just the cat code and no O2 sensor codes, then the O2 sensors are probably OK and just the cat has failed.
The PCM has to test the O2's first before moving on to the cat test. If the cat passes or fails its test then you know that the O2's have passed their test. Your OBD 2 tester may show monitors to tell you what tests have passed or completed. The cat is tested last.
The upstream O2 is before the cat and the downstream O2 is after the cat for the PCM to compare before and after readings. Each sensor has 4 wires, 2 for the internal heater, one for signal out and one for signal ground.
If you have no leaks in the exhaust before the sensors, then you don't have to worry about them setting false codes because of that.

 

[marcpilot1]

I reset the cel by doing what you said. Unhooking the jumpers. The light went off and still hasn't come back on. The obd shows no codes now. Weird. I just don't think it was fluke though. Even though everything is back to normal. No codes, no cel. Thanks for explaining where the sensors are. Will prob leave them alone though. And you're right about obd showing graphs. There's a lot of graphs. Wish I knew what to look for. Believe it or not, the info you give helps A LOT. I really appreciate it and will be back. Prob tomorrow when that cel comes back on. I know it coming. Thanks! Oh yea, there's this thing you can buy for about 60 bucks for almost any car made. It supposedly gives the car better gas mileage, more power by telling a cars computer something different. And it hooks up to THE computer in about 10 mins. Do you think its really what it says it is or a scam? Didn't want to say its name. Thx-

 

[Bob Lincoln]

Scam.

 

[ImperialCrown]

The automakers would already have built that product/software into the car if it really did what it said while meeting emission standards. Their corporate engineers and scientists are unmatched except for possibly the space program.
In today's horsepower/fuel economy wars, even being able to publish one more mile per gallon or a couple of more horsepower could be the difference between being a class leader and a class runner-up. The competition is very tight and some people shop by the numbers.
Having the engine in good tune, correct tire pressures (maybe a bit higher in the front), good alignment, current scheduled maintenance and smart and gentle driving habits are the things that you have control over.
I do agree that these aftermarket 'miracle' power and economy devices are a scam.
Our '98 JX gets around 22 mpg around town and has gotten about 30 on a trip. 2.5L is small for a 6-cylinder engine and the JX is a fairly heavy vehicle. Convertibles need the extra body structure reinforcements without having the steel roof panel in place.

 

[marcpilot1]

,Again, ya'll are dead on. I installed a mini trip thing couple days ago that IT got from a you pull it yard and it says I'm getting 23.5 mpg city, 28-30 hiway. Oh, that lil computer was easy to put in. I got one out of another 99 sebring jxi and took my bezell off, took the glass piece that protects the mph, gas gauge, rpms, and all that stuff around speedometer. Behind that was the wires with a taped wire and the plug just sitting there taped to the wires that go the trac off and odometer. Plugged it right up, used the black bezell from u pull it and bam, got a cmtc now. Ok, off subject, sorry. Mpg is fine without any 60 dollar gimmick. I wanted to say that the cel hasn't shown back up. And that's been a while now. No p0420 code either. So it popped up one day, I unhooked jumpers, that cut cel off and I haven't seen cel or got code on my obd2 since. Do ya'll know why it hasn't shown back up? Cat conv ok maybe?? Thanks!

 

[marcpilot1]

Yea, I'm gonna have to agree with ya on that part that's supposed to make any car et more horsepower and mpg. Scam was the right word I'm sure. I would like to know if anybody ever did buy one añd the results. Anyway, I laughed a lot when I saw that 1 word. Scam. That was pretty funny. And true I'm sure. Thanks, and that's sincere. A lot.

 

[Stratuscaster]

Those devices work on the principle of weight reduction.

By reducing the amount of cash in your wallet, the overall weight in the car is reduced.

 

[marcpilot1]

Absolutely! Ha! I know this, if you want the most miles you can get out of your car, tune it up, make absolutely sure the tire pressure is correct and WEIGHT. Get as much stuff out of the car that you can. Don't ride around with stuff you don't need. I rode around for about 2 months with my tool box in the trunk because it was really full so was heavy.Pus tools were locked and safe. Combined with the normal everyday things and the other once in a while stuff I tote the mpg were 21 or so. Well, prior to leaving tool box and stuff in car I was getting 32 or more. And that was on the in dash computer. So I thought it had broke or I was needing a tune up or something. Well, one day I had take all the stuff out of the truñk for some reason. The next day the in dash computer was back up to 33 plus MPG! All because I had weight in car. I learned. Thanks ya'll!