1999 VW Jetta engine codes

[j***@gmail.com]

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.

[j***@gmail.com]

Post by j***@gmail.com
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
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.

More info, it is a 1999 2.0L GL, new style. Thanks.

[dave AKA vwdoc1]

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
(One out of many daves)

Post by j***@gmail.com
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
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.

[j***@gmail.com]

Post by dave AKA vwdoc1
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
(One out of many daves)

Post by j***@gmail.com
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
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.- Hide quoted text -

- Show quoted text -

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.

[dave AKA vwdoc1]

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. :-(
--
later,
dave
(One out of many daves)

Post by j***@gmail.com

Post by dave AKA vwdoc1
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
(One out of many daves)

Post by j***@gmail.com
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
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.- Hide quoted text -

- Show quoted text -

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.

[Brian Running]

Post by j***@gmail.com
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
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.

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.

[Lost In Space/Woodchuck]

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.

Post by j***@gmail.com
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
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.

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.

[Brian Running]

Post by Lost In Space/Woodchuck
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.

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...

[j***@gmail.com]

Post by Brian Running

Post by Lost In Space/Woodchuck
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.

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...

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.

[s***@aol.com]

Post by j***@gmail.com
advice. And again, more info would be appreciated about rich/lean
faults.

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.

[Turtleguitar]

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.