oldracer

I am periodically getting the code for a failing cat so sometime before next year's CA smog check I'll have to get it fixed. Before that though I am doing some research and have some questions, here goes. I found the local CA Chevy dealers want an arm and a leg for the cat and labor to replace it. Both local ones said they will not sell one to me? So, I checked with Rockauto.com and they have them (Walker for example) for $160 but will not ship to CA so I could get my daughter in AZ to get it for me. Are these aftermarket ones as efficient as the ones from the dealer and would the "brain" be able to tell the difference?

I plan to do some driving with my AutoEnginuity software plugged in and watch the rear O2 sensor to see how it responds as many websites and a couple of friends told me the O2 sensor could be failing as the car has 126K miles on it. I would probably use a Bosch replacement as I used them in my race car and they worked very well over a long period of time. Is there any place that shows what the output of the rear O2 sensor should be if it is good as I have searched and did not find anything?

Finally I DO NOT plan on trying the lacquer thinner in the gas tank trick as seen on the net! So do not worry about that.

donbrew

DONOT use Bosch O2 sensors, or any other cheap ones, this is personal experience they do not read correct voltages.

It does not matter where the cat is shipped to. Unless it is labelled for CA it will not pass CA smog. Not legal for use on cars in CA is in the fine print.

My cat is P0420 and my new NGK sensor reads about .735V. For comparison the Bosch read about .2V and produced a low bias code.

oldracer

Thanks for the info. I plan to do a test run tomorrow on the way to class so what voltage readings from cat 1 and cat 2 should I be seeing if the cat is okay and the O2 sensor has gotten gooped with stuff from our wonderful CA gas?

donbrew

The #1 changes radically and really does not tell you much. The #2, well I am in the same boat; I tried to get info here with no responses. But, the "nominal" voltage for the #2 is said to be around .45V, that is what "everyone says" but I have no specific numbers for the HHR.

Lucky

It's not so much the voltage numbers but how fast sensor 2 moves from rich to lean compared to sensor 1. A good convertor burning the left over exhaust from combustion will make sensor 2 read much slower than sensor 1

When a convertor is no longer working well the speed of the sensors will become about the same indicating that the convertor is not burning and or converting exhaust gases.

One easy way to check the convertor is with a no contact thermometer. With the engine at operating temp the convertor temp will be much hotter than the other parts of the exhaust system. Like at least two to three times hotter

donbrew

"They" say that the temp differential test is no longer a valid test on 3 way cats.

The problem with checking the switching rate is that OBD on the HHR does not support it, so you need a very expensive piece of equipment and training.

The only thing we can do is compare the graphs of the #1 sensor (should vary greatly and often) and the #2 (should stay close to steady). At idle, BTW.

oldracer

Here is an update on the O2 readings. I ran the car for a while to get it nice and hot and O2 #1 voltage jumped from 0.09 to 0.79 as expected. O2 #2 was pretty stable at 0.79 to 0.82 and every now and then would drop down but recover so fast it was impossible to get a reading. This was at idle, constant speed at 30 MPH and some easy acceleration (no wide open stuff) so maybe it is the awful gas I buy at Costco as I have been using their 87 grade so I'll try some of the good stuff to see what happens? The O2 #1 status also said it was in closed loop which is normal.

Snoopy

Just so you know.....

Costco gas is TOP TEIR as of about 2 months ago. So it is no worse than Chevron, Shell, and others rated at the same level. In fact, as far as "cleaning" some interior engine deposits, it may be a little better since it has 5 times the additive over the mandated federal requirement.

I've been using Costco gas for years and have never experienced any problems. I also have many friends, including the Costco Store Director, who have performance vehicles and use Costco gas.

I even use it, via 5 gallon cans, when I hit the track.

My point in mentioning this is to inform you to seek other avenues to remedy your problem. It is not the gas......unless you pumped some that is contaminated.....which is highly unlikely because I know Costco's maintenance requirements.

donbrew

That's the same as mine. I have exhausted other possibilities.

If you turn the CEL off it will stay off for about 18 cold starts. But, it will still flunk emissions, as "not ready", because the EVAP will not have run.

oldracer

I read the sign on the Costco gas pump to day when filling up and noted the 5x info. As I have found over the years, it is best to eliminate items one by one and the gas is the easiest to check. So far I have about 20 starts on the car since the last time the 420 code was thrown so we'll see? My questions are what are the O2 readings that will trip the code and can the cat act just fine for a while and then decide to cause the code to catch? Same with the O2 sensor, can it be fine for a while then have an issue and what are the readings that cause the 420 code to show up?

I asked the mechanic that worked on my wife's 2003 Deville earlier this year and with that cat the code would clear and next start cycle come right back. He said normally the cat will go bad and stay bad all the time, not be good for a while and bad for a while? He said the same about the O2 sensors but if there was an electrical connector or wire issue then that could cause spurious failures.