Just got out of the shop. Guy said my right cat was running inefficient (throwing a P420). He said I should replace both front cats, because the new cat would probably cause the older cat to start throwing a P430. This is on a 2003 LS 430. Does this sound correct? Thanks!!

 

where that could be a possibility, sounds like he might be trying to get you for more labor. they are independent of each other, so labor shouldn't be any different doing it now or later. i could understand if one had to be removed to get to the other. but that isn't the case with this.unless he's cutting you a break on labor for doing them at the same time.

 

i should add....i'm not sure if there is a difference between 01-03 & the 04-06. my 05 the front cats are independent of each other.

 

These cars usually throw that code due to small leaks in the exhaust ahead of the rear O2 sensor. Have your mechanic or an exhaust shop look for signs of a leak. The cats don't wear out through normal use. If your car is running very rich it can destroy a cat but you would have other signs if that was the case. This code is thrown when the rear O2 sensor is detecting oxygen in the exhaust, usually caused by a leak upstream that is drawing the oxygen in. Another quick and cheap fix is to remove the offending rear O2 sensor and install a "spark plug non-fouler" and then reinstall the O2 sensor. It effectively moves the sensor out of the exhaust flow so it can't detect oxygen.

 

I ended up doing foulers on mine for both codes. The CEL comes on from time to time and goes away on it's own. I'm sure it still stores the code but I haven't checked.

 

Another thing to keep in mind is that as long as you are not trying to pass emissions this code will not cause any drivability issues and will not cause any damage to your car.

 

in my case, i had the code. i replaced the rear O2 sensor. the light was out, but then came back on about a week later. since my wife was driving the car, i let it slide for a couple years until the next emissions test was due. we postponed it a couple times. but now since i'm driving the car, i had the cats replaced, and the light went out on it's own.