The check engine light came back on yesterday and had autozone test it today and now it is the catalytic converter. How much does this effect the performance and especially the gas mileage. Performance/power is definitely up since tuneup but worried still about the gas mileage.

 

if the dtc was p0420 catalyst efficiency and no other dtc; it will not effect driveability. This dtc usually sets when the catalyst is no longer doing what is should...oxidation reactions of C0 and hydrocarbons.


the only problems a cat will cause is if its clogged or has broken substrate moving around; this will cause a exhaust restriction.

 

Error code-p0420 catalyst efficiency below normal (bank 1)

 

It's either the sensor or the converter itself. All it does is monitor converter efficiency, as stated. No effect on engine performance.

 

Just resetting the codes works many times.

 

TY. Hopefully it won't effect inspection in January.

 

If the check engine light is on, it will fail inspection. Start with replacing the sensor. If that does not work, time for a new converter.

 

Going to start with Lucas gas treatment with a full tank and run that a few days then reset the code and wait to see if it comes back on. If it does then on to the sensor. My mechanic explained to me that having a miss in cylinder three for sooo long could've messed up the converter.

 

He is correct. Sending unburned fuel from a misfire into the converter can ruin it in short time.

 

MPG done old fashion way and was 19.98mpg over 257 miles with about %60 highway use.