Catalytic converter

[HillbillyJake]

I was just wondering if there is a way to tell if the cats are going bad without a check engine light going on. I have almost 70k on my 08 Pathy and something seems a little off to me. I do not know if it the cold weather or something else. it seems like I have to give it a little more throttle than before to maintain speed and my fuel mileage also seems to be lagging. I am averaging about 13.6 to 14mpg. now that is a mixture of a 4 lane with stoplights and back roads. also the sound seems to be a little off as well. I read that the exhaust will have a sulfur smell to it. my question for that is would you be able to smell it behind the truck or do you have to get closer to the tailpipe. if there is a problem I would like to have it fixed before the warranty runs out but without a SES light on I am not sure. thanks in advance.

[driftedoffroad]

I first noticed my gas mileage diminishing before anything else. I checked my O2 sensor readings and the rear was basically stuck reading on the low side. Replaced the sensor and no change. It took about 20k or so miles to set the code. I am not 100% its the cat but thats my best guess now and what I will be replacing next. So if you tell them your gas mileage is poor and you suspect may be a cat. problem that may help. Good luck

[Tech]

Rear o2's should be steady and biased lean.

That's in fact the sign that the cats are working as they should be. You can go in and have a "mixture ratio test" and check the "alphas". The R51's have A/F sensors rather than the conventional front 02's, so the mix ratio test is a bit different. Then have them check s1 and s2 readings for B1 and B2. They should know what this all means. Do all this at operating temp. It's the best way to check other than check pre/post with a 5 gas analyzer (which has it's own issues).

[driftedoffroad]

I guess I missed one word. The rear was low on ONE side lol.