needed advise from the pros!

[bonnie02rkt]

Well I have ran into an on going issue with my bonnie. I have had the SES light on the dash and thought i could resolve the issue my self! It is the p0420 catalyst eff. below threshold. I took the first step of replaceing the cat. soon to see that a couple of months later the same code is back. So then i replace both the o2 sensors and no luck. and one more step that i felt would work is to use and apply the "PREVENATIVE MAITANENCE LIST" and of corse no luck. Finally got the INTENSE PCM with the o2 code delete and finally got rid of the SES light but I know I was still just hiding the real problem.

The real issue is that now I need to get state inspection with emissions and i FAILED due to O2 SYS not ready and EVAP SYS not ready.

My buddy said it could possibly be due to a cheap cat converter. I want to get a high flow but im not too sure cuz I know the computer is pretty picky. i dont know what to do next and im desperate for help to fix the problem and not just hide it. I would really like FEED BACK PLEASE!

[EWC88]

I am not positive on this but other's will shoot their advise or label if I am wrong or right, but I believe if you wanted to get Magnaflow high flow cat your going need the PCM programmed to accept it otherwise you have a 50% chance of getting the code again.

I got a magnaflow cat put on my SE and the code went away, now couple months later my SES light came back on throwing the codes, I just don't know if its because I didn't get my PCM programmed, or if the CAT is bad, or if I need to replace the O2 sensors.

[bonnie02rkt]

does any one else ahve any input that will help i need help!

[Archon]

Not having state inspections, nor needing to track down your particular problem, I can only take a few guesses at what is happening. It's possible that having the O2 code deleted from the PCM may also prevent the O2 test from running. That would give the not ready information to the scan tool. I believe the tests are run in a particular order, and if one fails or is not completed, the other tests won't be run. That could be why you're also getting that the evap test has not been run.

Your best bet to pass inspection may be to have a good cat put on, and having the O2 delete removed from the PCM.

[01bonneSC]

Canister purge solenoid got rid of my P0420 code.

[bonnie02rkt]

Well thanks; any good catalytic converter that doesnt have the history of throwing a code?

Oh and where is the canister purge solenoid and roughly how much do they cost?

[LeSabre in Buffalo]

Mine's on the front of the engine with a few rubber and metal lines running to it. Follow the vacuum fitting back from the throttle body and you'll run into it. It's a fairly cheap part, IIRC.

[Archon]

If you replaced the cat yourself, any good parts store should be able to advise you on a good one that will be an OEM type. If you take it to a shop...they should also. I had my high flow cat put on by Midas, who had some knowledgeable people and I have not had any trouble with it.

I don't believe the canister purge solenoid will help your situation. That would fall more under code p0440, or the check gas cap code.

Just to be sure, the car was fully warmed up when you had it tested?

[01bonneSC]

My magnaflow hasnt thrown any codes about 40,000 mi on it. Put it in myself.

[LeSabre in Buffalo]

Go to a different emissions station. IIRC you can have 2 emissions tests not run and still pass emissions as long as everything is in place, the CEL is not lit, the computer does not have a memory of that code, and the other tests are run. That's federal law, not state law. Find out how right I am (I'm in the ballpark), print it out and show them if they say every single test has to be run because it isn't so. I passed NYS emissions last year with 1 test not run after my battery died a week before my inspection.

[bonnie02rkt]

ah where can I get info on state and fed laws'; man my inspection is over due!

[Mechanical Mike]

Go to a different emissions station. IIRC you can have 2 emissions tests not run and still pass emissions as long as everything is in place, the CEL is not lit, the computer does not have a memory of that code, and the other tests are run. That's federal law, not state law. Find out how right I am (I'm in the ballpark), print it out and show them if they say every single test has to be run because it isn't so. I passed NYS emissions last year with 1 test not run after my battery died a week before my inspection.

In New York State you can have two tests not run on 2000 & older. 2001 & newer can only have one test not run. It's an EPA requirement so Texas is most likely the same. Keeping the gas between 1/4 & 3/4 of a tank may help get the EVAP test completed. This brochure has some tips on getting the test to run but they didn't help me. http://www.nydmv.state.ny.us/broch/c114.pdf It seems to take forever to complete the tests if its cold (below 40?) out. I doubt if that's a problem in TX.

[LeSabre in Buffalo]

Mike, one of the tests didn't run on my car for 2 weeks and 1000 miles until I got back down to SC.

The canister purge solenoid is run pretty often. I had a bad rubber fitting at the canister that went a week after inspection (whew!). The SES light came on immediately with a "large evap leak" code, and went off immediately after the fitting was replaced. I didn't clear it or do anything besides shut the car off, fix the fitting, and turn the car back on.

[geofffinlay]

You asked for a Professional opinion, here goes:

The Cat Efficiency code is caused when the REAR O2 sensor spends too much time reading above 500mv (rich). This is almost exclusively related to the condition of the Cat. When a good cat is operating correctly, the rear O2 will read below 500mv. In fact, you'll find that on a typical GM the voltage reading of the rear O2 (assuming it works correctly) will be very close to 200mv and be very steady. This indicates that HC at the Cat outlet is very low, just as it's supposed to be.

Your problem could be distantly related to an evap purge valve leaking, but if that is the case, the front O2 would be reporting a rich condition, which would set a (front) O2 rich code. I would certainly suggest that you don't spend any money on a purge valve until you have the problem with the Cat under control.

Here in the Toronto area, our Drive Clean management have issued bulletins to Repair Centers, NOT to install aftermarket Cats, I think you'll find sinilar bulletins in your area too. This is for 2 reasons. First, "most" are made very poorly and do not have sufficient material to make them work well (too long an explanation for this format). Second, they tend to last less than a year. We get the same aftermarket Cats as do you Stateside and have the same issues.

I'll add one more reason, from direct experience, in the case of GM V6 engines, even the best aftermarket Cats can be hit and miss to maintain their "lit" state, which allows the rear O2 to creep up above that 500mv range. Get hold of a scan tool and monitor the rear O2. If it doesn't spend more time low than it does high, the cat is your problem.

If your going to buy an aftermarket cat, get a written warranty (directly from the installing shop) that it will last more than a year. Also, pay to get it scanned before and after the Cat install.

Finally, you can force the car to run all its monitors by doing a "Global Drive Cycle". Google "GM Drive Cycle" and you will get a set of instructions to follow. You must follow them EXACTLY as it's laid out for you, including times,speeds and temps. If everything is working correctly, all your Monitors will be Complete/Ready and you'll ace the OBDII test.

By the way, someone has to train your local technician. I'm the guy that trains the guy that trains the tech.

Geoff

[01bonneSC]

Isnt the rear "O2" sensor technically a catalyst sensor?

[Archon]

In general, it is. It does get involved in a minor role for fuel delivery. This is part of the description for the rear sensor.

In addition to catalyst monitoring, the post-catalyst heated oxygen sensor has a limited role in controlling fuel delivery. If the post-catalyst HO2S signal indicates a high oxygen content or a low oxygen content for an extended period of time while in a closed loop, the control module adjusts the fuel delivery slightly in order to compensate.

[geofffinlay]

For a little clarification. The PCM's primary functions are to protect the cat and to produce an average air/fuel ratio of 14.7 parts of air to 1 part of fuel -(by weight) stoichiometric. Throughout all of the changing conditions, from cold to full warm & idle to WOT, the PCM is collecting information and calculating fuel delivery routines to keep coming back to that same 14.7/1 ratio overall.

At 14.7/1, both the engine and the cat are at their most efficient. Information from both upstream and downstream oxygen sensors, inform the PCM of the amount of oxygen passing by, relative to atmosphere. The less oxygen, the richer the ratio. If the post cat oxygen sensor cannot stay at the low end of the voltage scale it is indicating to the PCM that the exhaust is (relatively) rich (hi HC) at the Cat outlet.

The PCM can make fuel delivery adjustments based on the high HC readings, but if the Cat cannot control the HC level, it will set a Cat Efficiency code, generally after two drive cycles. The condition can be observed with a "proper" scan tool in Mode #6. The Cat Monitor will read as either NOT COMPLETE or NOT READY. This indicates that the PCM has noted the problem and has attempted to run that Monitor. When the test was not successful i.e. Post Cat O2 Voltage Threshold High, the Monitor was not completed. A second unsuccessful test will set a code and turn the C/E lamp on.

Many experienced techs aren't aware of Mode #6, so it's not expected that everyone reading this will know that much about it. You can find all kinds of interesting Mode #6 info on the net. Those of you not familiar, will get an real eye-opener when you realise how complex OBDII actually is. Have fun learning.

Geoff

[bonnie02rkt]

Thanks Geoff I really appreciate the info; I never thought of it that way that was really great! I will be looking forward to testing those systems and I hope its the cat. and if so do I just go with OEM or do you know if there are any other GOOD QUALITY cat. convs out there?

[geofffinlay]

You're quite welcome, glad to share. Re a good Cat. The original is the best way to go, but obviously way costly for what you get. I'd ask a local tech that's involved in both test & repair what's the best available for the price.

I think I'd tend to stay away from muffler shops, unless you know one well. It seems that they're set up to get you the cheapest possible parts, and that's not going to buy you a decent quality Cat. With Cats, the quality is in the construction and you really do get what you pay for. When you have a choice between two or more, go with the physically largest.

Geoff

[Oldman]

Geoff,
Thanks for the incredible amount of information!!
I've always been intimidated about this whole "converter/front O2 sensor/rear O2 sensor business, but now I think I can grasp it all a little better.
I'm in a state with no required inspection. What type of shop would be able to diagnose if my problem is the convertor or one of the two O2 sensors?

Thanks in advance!!

Also, If I remove the convertor and resonator (I simply can't afford to replace the CAT right now and my gas mileage is starting to decrease slightly) will I have problems other than the light staying on?

Thanks,