Catalytic converter

jetta
volkswagen

#1

The catalytic converter on our 2003 jetta gave out. We went to a chain store that had worked on the muffler previously. They installed a new converter and two months later the “check engine” light came on, with the code for catalytic converter (our regular mechanic checked the code for us). the chain put in a new catalytic converter and it ran OK for another 2-3 months before the light came on again. Should I continue to go back to them? Is there something quirky about Jettas? They told me they used a “direct fit” converter, which is what is recommended by VW and they are puzzled by why the light came on.


#2

There is no code that tells you that the catalytic converter is bad. Normally when people say that there is a code indicating a bad cat it is actually a code that refers to issues reported by and oxygen sensor. But there are plenty of reasons that the O2 sensor might not be reporting correctly (e.g. it is bad, it has a problem in its wiring). Find out what the actual code is and post it. I’ll take a wild guess: P0420 - have a look at this: http://www.obd-codes.com/p0420

It is also the case that the “direct fit” cat is probably an aftermarket part. Those are normally fine but some cars are picky in terms of having an OEM part. I don’t know enough to comment on that re: VWs


#3

yes, it was 420. what does that tell me?


#4

cigroller is correct. Try changing the rear oxygen sensor because THAT is the part that is sending the “Catalytic converter efficiency below threshold” message. If your car has over 100K miles, I would change BOTH oxygen sensors, front and rear…


#5

also, if it helps fill in the puzzle … I had the “downstream” sensor replaced last year.


#6

yes, the car is at 105K miles


#7

The web link I put up explains it. Has everything been checked for exhaust leaks? Has the coolant temp been checked (sensor & thermostat function)? Maybe that sounds odd but a faulty t-stat or temp sensor causes an engine to run too rich and that shows up in the O2 sensor readings. (In fact, if the replacements keep the light off for a while maybe you are running rich and that is killing the cats). Has anyone scoped the O2 sensors? The downstream sensor was replaced, but was the wiring for that sensor verified as reliable & intact?

It is still possible that an OEM cat replacement may be needed, but you can always cross your fingers that it is something else.


#8

the “check engine” light came on, with the code for catalytic converter

No code says replace the converter. It may indicate some possible issue with the converter or more likely a sensor related to the converter. In any case it should be checked to see what it really means.

If you don’t have the actuarial code, then stop by a local parts store and see if they can help you get the actuarial code. Many will do it for free. If so bring that code format: [P1234] and let us see.

A lot of converters have been needlessly replaced.


#9

Wow, cigroller, that link really does have all the answers. Fred, if you haven’t already done so, click on cigroller’s link (http://www.obd-codes.com/p0420), print the web page, and show it to your mechanic.

You might also consider finding a mechanic who is a better diagnostician. The people you have been going to only seem to throw parts at the problem.


#10

well, when the company put in the 2nd cat, they said that the downstream sensor didn’t look right. But to be honest, I was a little worried about whether they were just trying to get me to spend more money. So I told them not to replace it at this point. Thoughts?


#11

well, when the company put in the 2nd cat, they said that the downstream sensor didn’t look right. But to be honest, I was a little worried about whether they were just trying to get me to spend more money. So I told them not to replace it at this point. Thoughts?


#12

Yes, I have thoughts. I think you should do what I have already recommended above.

Have you clicked on the link and read the information on that web page? It has all of the answers you could possibly find for this issue online. Any additional progress will have to come from a mechanic with good diagnostic skills.