Catalytic Converter

[hr1940]

I need help again. Thank you for the help you gave me concerning the brake fluid. The mechanic told me the same things you guys said. It was checked yesterday and all is good. I had a catalytic converter put on 4 months ago and the check engine light came on. I was told it was the catalytic converter and I took it back to the place that installed it. He tried to tell me that the converter had burned because I have engine problems. I informed him that I have my car checked once a year and all recommended maintenance has been done, spark plugs and wires have been replaced, transmission has been flushed and I had synthetic put in and the car does not burn oil. He then said that it burned because I used gas with ethanol. The car is a 2000 Mazda 626 4 cylinder with 83,000 miles. He removed the code 1 week ago and it reappeared again today. He said that it was my cars fault and there is no warranty. I need to be armed with a good argument when I return. The car runs very quiet and smooth. Any help with what to say would be appreciated.

Thanks in advance

 

[daves87rs]

All gas has ethanol in it...if raw gas got in there, maybe. Something simply does not make sense.

I need to research further, but I can't see the cat being a problem in these cars.

Catalytic coverter issues don't usually involve something I would call good running.



Sounds like it could be something else....

 

[JHZR2]

Id say the mechanic is WRONG. Ethanol has nothing to do with it. Did you buy an OEM Mazda converter, or was it an aftermarket one?

An OEM will be $1600 or so, aftermarket somewhere between $100-500.

When I was having emissions problems, I got an aftermarket, and it only worked within a few ppm reading of the failed converter! It was that poor in terms of performance. Put in the OEM and the exhaust was SUPER clean.

So I have to wonder if you didnt get the best converter.

But before taking on the expense of the converter, Id want the car on a scope to check if BOTH O2 sensors are working. There should be one before and after the converter. If youre getting the converter efficiency code, which is what I bet it is, it could be that the rear sensor is working poorly and causing a discrepancy that it is blaming on the converter.

Hope this helps!

 

[crazyoildude]

Check this out but i believe that after market cats must be warranteed by federal law for up to 25,000 miles
And ones purchased at a car dealer 12 months or 12,000 miles..
Does the car have a mis fire or any other problems? Is the engine constantly at idle?
There are strict laws regarding cats in most cases... I will check tomorrow and let you know for sure. What code is present?
Also what State was this repair done in and is the car registered in the same state? You can e mail me if you like..

 

[expat]

I'd like to know what the OBD code was?

 

[hr1940]

They did not tell me what the code was and I could not read the code over the guys shoulder.

 

[bdcardinal]

If they put a real Mazda OEM converter in there it would have a 12mo 12k mile warranty on it. It wont cover labor, but it will cover the part.

 

[cmf]

The conditions to burn out a converter are very extreme. Regardless, it should still be under warranty and he would have to either replace it or prove that your engine is to blame. Most independent shops and dealers give 12 month/12,000 mile warranties on almost everything they instal.

And by gas with ethanol, he has to mean E85. And even then it'd be a very early failure for a car running E85 all the time. E85 can shorten catalytic converter life but not to the point of it lasting 4 months.

What JHZR2 said is also correct; aftermarket catalytic converters for the most part are awful. A lot of them specifically state that they are "low performing" and all but the most expensive are illegal to be sold in California. The catalysts put into the converters are very expensive and the cheap converters put in less catalyst which makes them function at a low efficiency but cost a lot less.

What it sounds like to me is that they installed a junky converter and it's not doing it's job well enough to keep the car from throwing a code.

 

[Nick R]

If it's a P0940 (I think) I had the exact same issue with the cavalier. After replacing the Cat with a Manaflow unit for $150 the CEL came right back on again with the same code, with brand new Oxygen sensors as well. Of course, this was about 3 days before the oil pump went, but that's irrelevant. Apparently aftermarket Catalytic converters suck.

 

[The_Eric]

Like others have said, most aftermarket converters are of very poor quality. While most will at a minimum last longer than 4mo, they are still sub par when compared to an O.E.M. part. The mechanic is just trying to weasel his way out of a warranty repair...

Another possibility is that the O2 sensor(s) are bad. A bad O2 can make the the computer think the converter is bad by reporting back false info. Stop in to your favorite mechanic and have him check them for proper operation.

 

[The_Jeff]

http://www.epa.gov/oms/cert/factshts/catcvrts.pdf

5/50 warranty on that cat. If your car didn't have a CEL for a long time that you ignored, it is defective.

EPA would not allow a fuel additive (eg ethanol) to be sold at retail if it damaged cats. Period. That's why they don't sell leaded gas anymore.

I would get the shop to put their denial and reasons for it in writing. Then call your state or the EPA.

 

[jim302]

Originally Posted By: JHZR2
But before taking on the expense of the converter, Id want the car on a scope to check if BOTH O2 sensors are working. There should be one before and after the converter. If youre getting the converter efficiency code, which is what I bet it is, it could be that the rear sensor is working poorly and causing a discrepancy that it is blaming on the converter.

Hope this helps!


I definitely agree on this. If the reading from an O2 sensor is wrong but sensible, it is definitely possible to get a catalytic converter code. This is more common with some cars than others.

As always, the code tells you where to start looking, and does not guarantee that the part it mentions is bad, but rather that more testing is required.

I assume you haven't had any misfiring, and the fact that the car doesn't burn oil either indicates that the engine is most likely in good health.

 

[mechtech2]

A cat code is often just the REAR O2 sensor being sluggish or faulty.
Since Mr. Doofus thinks ethanol is the problem [it actually helps, not hurts in this area], get another mechanic.
You could take a change with a new O2 sensor yourself, but there are no promises.
Internet diagnosis is tough.

 

[TooManyWheels]

We should put this in context for Helen -

The function of the first O2 Sensor (the ones before the CC) is to make the engine run as cleanly as possible by adjusting (basically) the fuel/air mixture, but other things also, depending on the vehicle. If the code given is from the front sensor, it could indeed be because of an engine malfunction (more than which the sensor can compensate for), or the front sensor itself could be defective.

The sensor behind the CC monitors the function of the CC itself by comparing the post CC reading to pre-CC readings. If there is not enough difference, (indicated by a trouble code) either the CC is not doing it's job, or the rear sensor is defective.

So the clue is which sensor is giving the defective reading. If the engine was "misbehaving", it would likely have made the front sensor go out-of-range, and the mechanic would have therefore fixed the engine problem or front sensor rather than replacing the CC.

Since he did replace the CC, that (should) indicate that the rear sensor gave the bad reading, meaning that either the CC or rear sensor is at fault.

He is now contra-indicating his own actions by blaming the engine for the problem, so he needs to explain which sensor is the problem, and if it is the front sensor, why he replaced the cat, and if it is the rear sensor, why doesn't he now suspect the rear sensor?

 

[The_Eric]

TooManyWheels, good explanation.



I'll add to my previous post that sometimes the O2 sensors can be damaged by using an air chisel/hammer to separate the pipes. I don't know how your car's exhaust is set up, but if the guy used one (air chisel/hammer), then it may well have damaged the sensor(s) to the point where they failed down the road.

 

[Vikas]

Most after market converters are not long term solution. Your mechanic should have known that. Bad rear O2 sensor is also very unlikely. Most O2 sensor become lazy as they grow older. They do NOT become hyperactive as they age. If the rear O2 is switching as often as the front, computer concludes that catalytic converter is NOT doing its job. In almost all the cases a dieing O2 sensor ends up NOT doing quick switching. As a matter of fact, the so called "O2 sensor extension trick" uses precisely this principle to get rid of P0420/P0430. It moves the sensor slightly away from the stream of the exhaust gases and makes the sensor switch slowly. This fools the computer in thinking that converter is doing its job. This is cheating and illegal but works. Also computer is tuned extremely aggressively as far as P0420/P0430 code is concerned i.e. way more stringent than the actual tailpipe emissions allowed by the federal standards. There are documented EPA studies showing that a typical vehicle with P0420/P0430 code passes actual smog test with flying colors.

Bottom line:- Forget replacing the rear O2 sensor and insist on getting them warranty their marginal converter. Unfortunately, the new aftermarket one will die soon too :-(

- Vikas

 

[hr1940]

I took the car back in and the check engine light had gone off on it's own. The guy said he can not get a reading when it is off. I told him to try and he showed me and said everything is normal now. He said I needed to fill it with premium and add a can of sea foam to the gas. Run 2 tanks of premium and then when the light comes on again to bring it back. I will play his little game for a while and keep you posted. Thank all of you for your help. Each of you has given me the information I need to counter his claims without being rude.

Helen

 

[JHZR2]

Im not so sure about the can of seafoam or the premium gas. Sounds like he is full of hearsay, probably thinking that the premium has more cleaning agents in it (which it may) plus the seafoam.

I'd consider using the premium if your owner's manual states that the engine can use it. I'd prefer to go get a bottle of real chevron techron or gumout regane and run that rather than a bottle of seafoam.

You can claim all day that you did what he said, but Im not keen on that advice. It may be more stressful on the oil and engine (a lot of solvent) than you need to be. The other cleaning agents are designed to clean thoroughly. Ive also seen that seafoam can be hard on O2 sensors and cat converters.

My advice is that since Autozone seems to scan them for free, if you get one, get to the closest place that scans codes ASAP and get them written down but not cleared. Then get to the mechanic when you can. Post the codes for us when you get them.

 

[mechanicx]

Originally Posted By: Vikas
Most after market converters are not long term solution. Your mechanic should have known that. Bad rear O2 sensor is also very unlikely. Most O2 sensor become lazy as they grow older. They do NOT become hyperactive as they age. If the rear O2 is switching as often as the front, computer concludes that catalytic converter is NOT doing its job. In almost all the cases a dieing O2 sensor ends up NOT doing quick switching. As a matter of fact, the so called "O2 sensor extension trick" uses precisely this principle to get rid of P0420/P0430. It moves the sensor slightly away from the stream of the exhaust gases and makes the sensor switch slowly. This fools the computer in thinking that converter is doing its job. This is cheating and illegal but works. Also computer is tuned extremely aggressively as far as P0420/P0430 code is concerned i.e. way more stringent than the actual tailpipe emissions allowed by the federal standards. There are documented EPA studies showing that a typical vehicle with P0420/P0430 code passes actual smog test with flying colors.

Bottom line:- Forget replacing the rear O2 sensor and insist on getting them warranty their marginal converter. Unfortunately, the new aftermarket one will die soon too :-(

- Vikas


I agree with your explaination. The downstream O2 sensor code is usually due to the cat and not the sensor. Although if the wiring harness or wire insulation is damaged or the exhaust or downstreaam O2 has leaks that could possibly set the code. But that's not the O2 sensor being at fault per se.

 

[Vikas]

Certainly, we all owe a *lot* to Helen for providing us this forum. Can somebody who is in the area put a real scanner on her car and get the data? Just select front and rear O2 sensor reading as live data stream and have your scanner plot them. It will be pretty obvious then that the converter is not doing its job. After the engine is at operating temperature, take it on highway, keep steady 55 mph for a minute and then let it coast. Generally, at this time computer will most likely throw P0420 code when it sees both front and rear are switching at the same rate.

- Vikas