P0420 CEL ON!
 

Well, it happened yesterday.
CEL came ON but there was no change in performance though.
Hooked up the scanner and got 1 code P0420.
Immediately went to auto parts store and got new Autolite spark plugs and jumped on replacing all four plugs.
Spark plug holes were dry and no trace of oil.
Checked for vacuum leaks and all is well.
Reset the CEL.
So far P0420 has not come back after 100 miles.
Crossing fingers for code not to come back.:biggrin:

CEL came back ON. Drove the car to lunch and I only put in 50 miles after the reset.
Next thing to do is get some CRC mass airflow sensor cleaner and clean the @#$t ouf of the MAF and hope P0420 does not come back.

If it does comes back, I have to look for my spare MAF that came with the engine I bought and replace that. It is somewhere still attached to the intake manifold. Hopefully I don't have to.

I found my spare MAF, cleaned it with CRC MAF cleaner and installed it.
I need to get this car ready for emission testing before August 23 so the CEL needs to go away.

If I can get drive a full tank of gas without triggering the CEL I should be good for the emission test.

isnt' that the code for a faulty cat? maybe time for some new o2 sensors.. I had this problem show up on my 99 crv last year, after changing the cat for rust issues, got new sensors but not long after, it started coding, changed the sensors on garantee and after tests, we changed the cat again and that solved it. Before finally finding out that the cat was bad, I learned that you need to run the cat hot on it's first run to set it properly, so it "pops" into place,... or something, but it worked for me. fyi

You dont need to do a full tank of gas, you only need to do a drive cycle. google it, you will save yourself a tank of gas.

It's probably the reason your cars CEL did not come back on right away. A drive cycle is about 50 miles in an ideal situation.

Anyway, Good luck. If your other air mass sensor is no good, let me know. I can let you barrow mine to pass the inspection or sell it cheap or something.

Not sure if this will help: http://www.318ti.org/forum/showthread.php?t=35885

Great. Thanks.

Found this document online.

Replaced the MAF with a used one that has 90k miles yesterday.
P0420 came back ON this morning on the way to work after 120 miles.

It looks like I need a new catalytic converter.
Time to drop and clean the cat and do the subframe bushings.

Getting a new Cat converter to work is not an easy task. Check on here to see what brands worked for people. I know about 99% of the aftermarket ones that are suppose to replace our Cat Converter only work for about a week and then the CEL comes on. You do not want to drop $300 - $700 for a converter that breaks right away.

Your best bet may be to pick up a used one. If you look nearby, you might be able to get the entire assembly cheaply from someone who is parting out their car and you wont need to weld anything. If you cant get one, people will ship you cut sections of them.

Best of luck.

That may be my best route, a used one from car getting parted out.
There's really no change in performance, it's just annoying to see the CEL.

This used to be my daughter's car in Atlanta where there is emission testing.
I may have to register it here in Leesburg where there is no emission testing.

I just need to find a used cat.
The O2 sensors have never been changed and the car now has 237k miles.
Do you think a new O2 sensor might clear the code?
I am quite sure a new O2 sensor will read better and might trigger the same code. LOL.

You might be better off buying a used cat converter from someone who will give you the O2 sensors for free. O2 sensors are expensive but you can sometimes get them used with the cat converter for less than the price of new o2 sensors.

I think you can clean them, maybe try that first. I never tried it, but it might be the cheapest next step.

I found a used cat and the guy wants $150 shipped. It has 150k miles and still wants a lot of money.
Anyway, I reset the CEL and cleaned the MAF again while trying to decide to buy or not to buy the cat. So far I have driven 160 miles with no CEL. I also started using 93 octane gas. My daughter has been using 89 octane gas if that matters.

P0420 has not come back.
But P0130 showed up last week.

Went ahead and replaced upstream and downstream O2 sensors yesterday.
O2 sensors were original with 238k miles so they were due for replacement.
So far no CEL for the last 200 miles.

Awesome to hear.

As a side not, I just got the p0420 code yesterday. Go figure. My E46 has 248k miles and I am betting those sensors are original. With that millage and 4 sensors to replace, it will be a tough choice for me. Take care, update us if anything changes.

No CEL as of today.
P0420 fixed itself by cleaning MAF and using 93 octane gas.
Thank goodness I don't have to replace the catalytic converter.

P0130 has not come back after replacing before and after cat O2 sensors.
It runs really good. Throttle response was better with new O2 sensors.
I am averaging now 31 mpg city. It used to be 29 mpg with old sensors.

Still no CEL. Great!
P0420 has not come back ON. (Replaced MAF with used one with 90k miles and cleaned it with CRC cleaner)
P0130 has not re-appeared also. (Replaced 238k mile two O2 sensors) (direct replacements from Advance)

I am happy and it's ready for emissions testing and tag.