This is on my friends 99 VW jetta 2.0L 4 cylinder gas motor with 100k miles. The check engine light came on and he took it to a shop and was told the before and after cat 02 sensor need to be replace ( $500)..I advise him to get the code pulled at autozone which he did and it said bad cat converter..Is there any way we can do to find out if its the cat or the 02 sensor for sure?? thanks for any help..
Emission related Problem on a VW
- Thread starter stang5
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O2 sensors run about $100 each for these cars, so is there $300 worth of labor needed?
Autozone does run codes, but they often can't narrow down to the particular component, only the system. I'm not surprised that they said bad converter, but there are other parts to the system.
Example is they will read a code that says something about "egr flow insufficient" or similar. They immediately say it's the EGR valve, most cases it's not, it's the DPFE (or whatever the letters are) sensor that controls the EGR.
In many cases, at about the 100K mile mark, the O2 sensors can get a bit "lazy" in reacting and can cause the CEL to come on. A good diagnostic scan can show the individual O2 sensor operation/voltages. If I HAD to pick something to replace, it would be the front (pre-cat)O2 sensor since it's the one that sends control signals to the PCM. The rear sensor is usually just a checking sensor.
Recommend either getting a software diagnostic for your laptop (got mine from Harrison research) or getting a better scan done at another shop before throwing $$ at the car.
Autozone does run codes, but they often can't narrow down to the particular component, only the system. I'm not surprised that they said bad converter, but there are other parts to the system.
Example is they will read a code that says something about "egr flow insufficient" or similar. They immediately say it's the EGR valve, most cases it's not, it's the DPFE (or whatever the letters are) sensor that controls the EGR.
In many cases, at about the 100K mile mark, the O2 sensors can get a bit "lazy" in reacting and can cause the CEL to come on. A good diagnostic scan can show the individual O2 sensor operation/voltages. If I HAD to pick something to replace, it would be the front (pre-cat)O2 sensor since it's the one that sends control signals to the PCM. The rear sensor is usually just a checking sensor.
Recommend either getting a software diagnostic for your laptop (got mine from Harrison research) or getting a better scan done at another shop before throwing $$ at the car.
mebbe apples and oranges ,but an O2 sensor in my 88 Bmw and at least early 90s fords can be tested with a voltmeter. The voltage runs .1-.9 volts and should change rapidly, when the exhaust mixture changes. The rapid change is the key. I created a vacuum leak and plugged the fuel pressure regulator to create the changes in the exhaust. There are more details. I googled for a few minutes to learn about them. Tested and found that indeed the O2 sensor was shot. Small wonder at 280k
Here's the thing to do:
get the car scanned with a VW specific tool and you'll get a 5 digit code much more accurate than a generic OBD2 code.
Go to TDIclub.com and look for the VAG-COM list and find someone in your area with a VAG-COM and get them to scan the car. This will tell you exactly what component has failed. Normally it costs you nothing or possibly a 6-pack of suds. If you want to get fancy then you can monitor all of the devices and see exactly why they're failing and what performance parameters are being fulfilled and why the code is being set.
Good luck with the issue. Since the 2.0 liter engine is a known oil burner then you may have a catalytic converter problem but you'd know if you've been having to add oil regularly over the past 7 years.
get the car scanned with a VW specific tool and you'll get a 5 digit code much more accurate than a generic OBD2 code.
Go to TDIclub.com and look for the VAG-COM list and find someone in your area with a VAG-COM and get them to scan the car. This will tell you exactly what component has failed. Normally it costs you nothing or possibly a 6-pack of suds. If you want to get fancy then you can monitor all of the devices and see exactly why they're failing and what performance parameters are being fulfilled and why the code is being set.
Good luck with the issue. Since the 2.0 liter engine is a known oil burner then you may have a catalytic converter problem but you'd know if you've been having to add oil regularly over the past 7 years.
Post back with a specific POxxx code, someone who knows VWs can help you more.
Generally, a temporarily rich condition is allowed for the cat to "fix" and the downstream O2 sensor "sees" it fixed. If the downstream 02 is not functioning well it will fail its own diagnostic and the "cat readiness monitor" will not be ready-- but you won't get a CEL for the cat, just the rear 02.
My bets are on the catalytic convertor itself.
Some shops are stuck in the 80's and will throw an 02 sensor at a CEL without really thinking too much.
A respected name brand service manual for your VW (I'm General Motors and proud so I can't help you much) or a VW specific forum will help you more.
Generally, a temporarily rich condition is allowed for the cat to "fix" and the downstream O2 sensor "sees" it fixed. If the downstream 02 is not functioning well it will fail its own diagnostic and the "cat readiness monitor" will not be ready-- but you won't get a CEL for the cat, just the rear 02.
My bets are on the catalytic convertor itself.
Some shops are stuck in the 80's and will throw an 02 sensor at a CEL without really thinking too much.
A respected name brand service manual for your VW (I'm General Motors and proud so I can't help you much) or a VW specific forum will help you more.
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