1999 VW Jetta engine codes

Looking for opinions, I have an issue where the check engine light is coming on. I recently gave the car a tuneup which cleared the misfire
codes it had, but now (1 week later), I have the following codes present:
P1128 Long Term fuel trim too lean P0172 System Too Rich P0134 Oxygen Sensor Circuit - no activity detected (pre-converter sensor)
I am guessing that the O2 sensor needs to be replaced, but will this also fix the other codes? I haven't detected any vacuum leaks that might be suspect. Any help would be appreciated. Thanks.
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On Mar 8, 12:33 pm, snipped-for-privacy@gmail.com wrote:

More info, it is a 1999 2.0L GL, new style. Thanks.
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That P1128 code would lead me to believe that there is a vacuum leak.
What is the mileage? The 02 sensor will get sluggish as it gets older. It could possibly solve your problems.
Are you using a tool like the ross-tech.com scanner? AFAIK It will allow you to see what the 02 sensors are doing. It should also give you a little more info on those codes too! ;-) I would want to check the Coolant Temperature that the ECM sees though.
--
later,
dave
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The mileage is only 57,850 miles. The scanner I'm using is an Actron OBD II scanner. I'm going to change the O2 sensor later todat and see if that works. Thanks.
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I would prefer if you had an imitation ross-tech.com scanner. The vag-com scanner tool copies can be had from Ebay for under $30 and will tell you more than a generic OBDII code reader. AND allows you to do MORE! ;-) More like Throttle Body Adaptations, read information from the ECM like coolant temperature and 02 sensor readings, troubleshoot problems by testing some components independently and get more info with the DTCs.
Let us know how the 02 sensor works out for you. 57,850 is low mileage for the 02 sensor and it might have been under warranty if the vehicle was less than 7 years old and under 70,000 miles. I believe you just missed out by 1 year. :-( I dislike guessing since it costs too much. :-(
--
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dave
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I'm not like a lot of the guys here -- just dumber, probably -- but I tend to go with hunches, if they're supported by any evidence. In your case, a dead O2 sensor would affect fuel mixture, so that would say to me, "Go ahead and replace the O2 sensor and see what happens." Odds are, it will fix the problem. If not, you can at least tell yourself it was not a total shot in the dark, it was a supportable decision, and what the hell, it looks like you needed a new sensor anyway.
I went ahead and replaced a mass-airflow sensor recently, due to a fuel-mixture code. They have a reputation for failing, so I rolled the bones. Sure enough, it did the trick. There's still room for seat-of-the-pants mechanics in this computerized age.
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Could still need a O2 sensor, but if it's too lean the O2 will not produce any activity... thus the fault. He needs to fix the lean/rich faults first.

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Okay, but -- and believe me, I'm not arguing with you, I know you're a VW tech and you know your stuff -- how do you fix the lean/rich faults first? I suppose there any of a number of problems that could be the cause, and it could take any amount of time to find them. An O2 sensor is easily located and replaced. No need to look any further, not time-consuming at all. As I said, it's at least logically related, so what the hell, replace it and play the percentages. If it works, then you're all done. If you don't have a good reason to believe the various codes are related somehow, then no, you don't just take blind stabs in the dark.
Someone with access to all kinds of diagnostic equipment and having all kinds of specialized skill and experience, well, that's another matter altogether...
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Good question, I have no idea how to fix the lean/rich issue. I do know that I replaced the sensor and haven't seen the light come back on. The engine is running smooth, and I have gotten the car to the proper temperature for the sensor to generate an output. I will keep you guys posted if the light comes back on, thanks for all the advice. And again, more info would be appreciated about rich/lean faults.
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wrote:

http://www.obd-codes.com/trouble_codes/generic/p0172-system-too-rich-bank-1-oxygen-sensor.php the link above is some info on the 0172 code
below : meaning of p1128 and a link for a bit of info on it P1128 Long Term Fuel Trim B1 System Too Lean http://www.obd-codes.com/forums/1709-obd-codes-2001-vw-jetta-gls-18t--5-speed-quottrouble-code-1128quot.html
Both codes can be caused by vacuum leaks it sez. I'd start there.
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replying to jhutchcraft, Turtleguitar wrote: I have a 1999 jetta, Every time it throws codes Pll28 and P0171 or P0172 I have to change the MAF sensor and it runs great again with no codes. I have had to change the MAF 4 times in this jetta.
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replying to jhutchcraft, Turtleguitar wrote: I have a 1999 jetta, Every time it throws codes Pll28 and P0171 or P0172 I have to change the MAF sensor and it runs great again with no codes. I have had to change the MAF 4 times in this jetta.
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