I have a 1998 Honda Accord EX, 4 cylinder with 156, 000 miles. For the past 18 months the Check engine light has been on and off. Recently the check engine light has been staying on.
The light first came on for the previous owner – around 130,000 miles. Indication was the catalytic converter was the cause.
The engine runs smooth. Idles smooth, accelerates well, etc
It does consume a small amount of oil – less than ½ quart for 3,000 miles.
The tail pipe does have a little more carbon than on my 98 LX with 107,000 miles. I can still see the metal through a light coat of carbon.
Today I took the car to Auto Zone for diagnostic of the check engine light.
Following are the results:
P0420
Definition
Catalyst efficiency low-bank 1
Explanation
The Oxygen sensors monitor the catalytic converter’s ability to store oxygen.
Possible Causes:
1 – Catalytic converter defective (failure possibly due to #2, #3, #4)
2 – Engine Misfire or running condition
3 – Large Vacuum leak
4 – engine oil leakage into exhaust – valve guide seals, piston rings

QUESTION:
How do I further diagnose to determine whether (1) the catalytic converter is bad, (2) the oxygen sensor is not defective, (3) I do not have a Large Vacuum leak, or (4) some other problem.

 

if it was misfiring it would run like crap
if it had a huge vacuum leak it would run like crap
it would have to burn more oil than that to set it off.

my guess is its just a bad cat

 

Thanks for the response. I been told sometimes the sensor goes bad and causes a false cat reading? How can I rule that out.

If it is a bad cat, are there any instruction writes-ups on replacing he cat. Looking at it, it appears that I should be able to unbolt at both ends, disconnect the wire to the sensor, then install the new one.

 

Shake/bang your cat. You should not hear any rattling. If you do, it is bad.