Chevy & GMC Vans

Hi guys, the Check Engine light popped up 2 weeks ago, and it read Catalytic lo efficiency. I cleared the code, and it has now popped up a week latter again. I replaced my cat with a Magnaflow High Flow converter last summer and I find it hard to have gone already, I thought it would have outlasted the life of the vehicle. Any thoughts? And my car is AWD, so it will be a PITA to replace again, plus costly. If it is in deed the cat, what are the effects of not replacing it till Spring, and if I do what should I replace it with? Cheers!

Sounds to me like you have a sensor gone bad. If the cat has been replaced there should be no reason it failed, unless your putting certain addatives in your gas or running leaded/race gas. I'd start with the sensor myself but thats just my 2 cents.

I did a little research and I found out that it is not the cat. Appararently the code Catalytic Inefficiency on the post cat 0xygen sensor: P0420 (cylinder 1-3) can be fixed by:

WHY: The reason why your OBD-II diagnostic systems report this error code is because the 02 sensors detect an above normal exhaust reading when compare to OEM catalytic converter. The OEM catalytic converter does an excellent job at filtering/cleaning/converting exhaust fumes into cleaner air. The DME/ECU calibrates its post-cat sensors to the OEM catalytic converter performance and specs. Therefore, aftermarket cats do not clean well enough to satisfy the catalytic efficiency monitoring of the DME. This is a very common problem with aftermarket cats especially the high-flow ones.
An "inefficiency" reading does not mean that your catalytic converter is broken especially if it is brand new. Again, the error codes just means that they are not performing as efficient enough to meet OEM standards.

SOLUTION: There are three feasible options to solve this inefficiency problem
Ignore.
Spark Plug non-fouler (aka Spark Plug defouler)
Software upgrade

This website shows you how to do the spark plug non-fouler:
http://forum.e46fanatics.com/showthread.php?t=486937

I have a friend who is a G.M. mechanic, and he asked me a question when I told him I was putting a 2005 5.3L V8 in my Astro. He asked if I was putting a factory exhaust pipe with cats, or an aftermarket set. I asked him why, and he replied that recently, he installed a complete Magnaflow performance exhaust on the boses new 2009 Corvette. He said that the O2 sensors detected a malfunction of both cats, and he determined that the readings being generated by the after-cat O2 sensors did not fit the values set by the Factory, in the PCM program. He suggested that if I wanted to use an aftermarket set of cats, that I should have my PCM reprogrammed to bypass the after cat O2 sensors only, and leave the pre-cat sensors in the program. The pre-cat sensors operate the fuel management system efficiently, and should not be disabled.

Well I finally had a chance to put the spark plug fouler on. This was put on the downstream 02 sensor. I drilled the fouler out till the tip could of the sensor could fit in. Only snag I had was trying to remove the old O2 sensor was extremely difficult and of course the threads got stripped trying to take it out. So I bought a new Bosch Universal 4 wire to replace it. So after I installed everything I ran up to Advanced auto and borrowed there OBDII code reader, cleared the codes and so far so good... Hopefully it won't be rearing its ugly head again anytime soon.

good report, i hope the fix sticks.

I'm looking to install the Magnaflow converter on Green as the stock one is rattling and the van is setting code due to it. I need to keep codes from setting to pass emissions. Has the defouler continued to do it's job?

I saw my last post was in Feb, wow how time flies by. And the answer to your question is that the S.P.F. is still working. No codes have been tripped since. 6 months is solid, def think it's the answer if the problem arises.

Excellent