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Discussion Starter #1
ok so i have a 2002 337 1.8t i have a p0420 code that keeps coming back well i installed a new turbo to bumper exhaust and im still getting the code so i looked at the data with my modis and i have a 0.00 readin on both short and long trim up and down stream sensors no matter cold start wot idle nothing changes they stay at 0.00 i dont know the Mk4 plat for so im here asking for some advice. im a mechanic and have the tools so please not dumb down any responces. thank you!!
 

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Are you reading live data or a freeze frame shot?

Does it go into closed loop?

What about O2 voltage readings? What do they look like?
 

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I would say ground issue i had a 2001 a4 with the 1.8t and thats what it was. I ended up replacing the harness for both up and down stream and then got my normal readings.
 

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P0420 code is usually caused by more exhaust flow. It's just an emissions related code. I had it when I put a larger exhaust on without a cat. converter. Most people run an o2 spacer or code it out with software.
 

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Discussion Starter #6
ok who offers a code out program that will allow me to pass nysi and this was on before and after i replaced the cats.. also i think the 0.00 read out on the data streem from the o2. has something to do with it. i have a year to solve this issue so im looking for all options. i also installed a 3 in stainless systerm that its a cat cut out for the car from vw proformance. and its still there. i have heard that the secondary air system can cause this code as well
 

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someone with vagcom can code out the 02 sensors i believe. unitronics stage 2 codes them out too.
 

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Discussion Starter #9
ok not to be and ass but twice O2 spaces have come up and i dont quite understand hot a spacer is going to get me a reading my modis says that the o2s read 0.00 and short and long term trim is 0.00 in closed and open loop. so how a spacer is going to change that i have no clue but someone please enlightin me
 

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If the only code you are getting is p0420 then I would not worry about the readings. Especially if the car runs fine.. the spacer will pull the o2 sensor out of the exhaust stream tricking the ecu. The code is usually eliminated. I have no clue why you are not getting any readings. Seems to me that if the o2 sensors did not funtion, the car would not run well. The upstream sensor is used for air/fuel ratio. That one should have a reading. The one after the cat is just for emissions. I had mine coded out and completely removed it. No cat. No o2 sensor.

This is how readiness looked in vagcom

When I did have an o2 sensor, I ripped the wires from it dragging on the ground. I then got a short to ground code. Since it was the post cat. Sensor it had no effect on how the car ran. Never checked the readings. Are all your wires intact?
 

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Discussion Starter #11
wires are entact im going to test the voltage and continuity of the sensor to see if its shorted inside. but i also noticed today when i was changing a fuse for my 12v socket i have a cut brown wire about the fuse panal behind the cover on the drivers side dash. i dont see another end to it ill get a picture to show and see if maybe that part of the issue.
 

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Cut wires are scary. Who knows what the previous owner did. Is the car modified in any way?
 

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Discussion Starter #14
ok so i got some new pictures and i finely got a reading from my forward o2. and the light skip i had went away. i still have no down stream o2 reading tho. i grounded the ground i showed earlier. what it changes ill find out soon but the car seems more responsive for sure. now where can i get a unitonics tuner soft wear file for a stage 2 or 3 i dont have a dealer with in several hours on me and im not really looking to have to drive.
 

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the first o2 is the one that matters. the second wont effect gas mileage or anything,
 

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stop playing guessing games re wire the harnesses in see if it makes a difference make sure to match up each wire correctly and use butt connectors that have the glue in them there the best if not use solder and heatshrink tubing but your problem is in the wiring and your ground if after your done wiring those in and you have the same problem then your problem is a main harness ground which youll have to go looking for a rusted or corroded bolt somewhere underneath the carpet or by the interior fuse panel clean the metal and the metal connectors then re diagnose ive had this same problem at the shop i work at twice now and i did this and it fixed the problem if the p0420 code comes back then most likely your cat is shot and you will need a spacer or replace the cat .. at this point id worry about fixing your o2 sensors get two new sensors and harnesses and put em in if the code comes back then put the spacers in.
 

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Discussion Starter #17
my car came from flordia there is no rust on it. and i didnt brake the wires. i know the cel is for a 420 because i have no cat at this point. my issue comes when i need to get an inspection in the state of ny you cant have the light on. i do believe the exhause system i got had a spacer honestly im looking to code it out. but i dont know where to go to get a good reliable ecu program. also i didnt ripe the wires on my car that was someone else showing my theres was ripped. as you can see its just flat lined on the moniter and thats the newest computer Snap-on offers we bought it last week for a tune of 10k + or - a k. also i think the o2 needs to just be replaced because its dented pretty good.
 
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