have 2004 accord exl 4cyl with check engine light on Advance Auto got code p0420 replaced cat and down stream oxygen sensor cleared code at approx. 170 mlies light comes back on Advance Auto checks and gets same code. what else could I try?

 

Is there anything wrong with the car while driving? Replacing Cat Conv. and Oxy Sensor must be $$.
But that suggests good for you; I just don't really have those $$ as easily available.



My '97 has been driving very fine (w/ good mpg) this entire month with check engine light on.
So, unless I have a driveability issue, I look at the CEL as a 'Clear Et Later' light.
My $.02

 

DIY price not nearly as bad as shops. The car runs fine no issuses no exhaust leaks but with the light on it fails nj inspection that is my headache thanks for the reply

 

Have you checked for exhaust leaks? Intake manifold leaks.

P0420 is the second O2 sensor detecting a problem with the amount of oxygen in the exhaust after the catalytic converter. Over 90% of the time, replacing the catalytic converter will fix the problem, but other items can cause this to happen. I would start with the basics first like running some fuel system cleaner like the chevron techron stuff. How many miles are on the spark plugs? Have you inspected the air filter?

 

Look for a large vacume link..take a spray bottle with water in it and start spraying water on all vacume lines you can see and look for water bubbling and listen for it snapping when you hit any leakage areas in the vacume lines..when you hear it you'll know what I am talking about..Yes..you have to have your motor running...

WheelBrokerAng

 

plugs and air filter were replaced at 126k three months ago. The car runs great its just that darn light/code. I will look again for vacumn and exaust leak thanks for the advice