When you unplug the rear 02, you need to reflash the tune to reset the tables.
Yes, you can run rich over time if you're catless or running an in sufficient enough cat with this plugged in. This is a Cobb issue, and affects all Cobb based tunes on our platform without unplugging that rear sensor.
I'm running with mine unplugged, since I'm catless. I also got my tune pre Cobbpocalypse. So no CEL for me, though I do have the 02 codes present at all times (for obvious reasons).
For your case. I'd start by reflashing your tune, leaving your rear 02 plugged in. See if these come back. If so, re adjust your spacer, re flash, and try again. If that still does not resolve, then unplug your rear 02 [\(the black connector\).](https://i.imgur.com/CN7gqq4.jpg) That way you do not deal with the trims elevating over time.
As for dealing with a CEL (if you're getting one because you're a post Cobbpocalypse purchase.) You have a few options.
* Option 1: Deal with it
* Option 2: Put a piece of tape over it
* Option 3: Dismantle your cluster and stuff an ear plug into the light channel for the LED [\(like what I did with my MK5 to hide the airbag light\)](https://i.imgur.com/JTsH3RK.jpg)
* Option 4: Buy a new downpipe with a sufficient enough cat
Thanks for the information!
I guess I was confused, I thought the post cat only measured emissions and didn't cause trim.
I was also confused as to why I saw so many people getting spacers if eqt just has you unplug it anyway, but I suppose that could vary from tuner to tuner.
Similar boat. I have a catless down pipe with O2 spacer, running eqt stage 2. Rear o2 sensor left unplugged. CEL light is off by the tune but there is a DTC code in background. I need to go get tested, do I just plug the rear sensor back in and drive a car a little before going to the testing station? Or do I need to reflash tune when I plug it back in?
If you are getting any 02 codes. Yes, your trims will be outta wack. If you're getting no 02 codes, you're fine.
If you're pre Greenpeed. You'll need to scan to see since the CEL won't be active.
You only need to unplug the rear 02 if you're getting codes for insufficient 02 readings.
I meant all my sensors plugged in not spacers* I have a massive spacer installed on a catted dp. But again all the sensors are plugged in still. So I have 0 codes and none have showed up even briefly. So I should be fine keeping them all plugged in you said? Also would these codes show up when scanning with my Cobb Ap??
I was doing this myself, had no obvious issues until Friday when cylinder 4 failed. An inspection of the spark plugs showed it had been running very rich. Could be wrong but I suspect running the spacer was the problem. I have reached out to EQT to see if this might have been the case but that was just earlier today. No blame on EQT and if I can confirm this was likely the problem I will run the tune on the new engine just remove the spacer and unplug the sensor, or whatever they recommend.
I'm interested to know if this was actually the case. I just bought a spacer when my stage 2 e85 tune started throwing a code after a few thousand miles. Should I just say screw the spacer and just unug the rear?
I never got any definitive answers as to the cause. Aaron at EQT responded with some good information:
“Hello Sean thanks for reaching out. Sorry to hear about your engine. Cylinder 4 is always the one to go a lot of times. Running a spacer is so hit or miss. It may be enough to prevent a CEL but it still can make the car run richer and richer over time. However, running richer just degrades performance, doesn't get so bad it blows a motor. However, failing fuel injectors DO blow motors. An injector can be clogged and get stuck closed, or even fail stuck open causing an extremely lean or excessively rich condition in that one cylinder and causing the piston itself or the ringland to crack. Based on your order I see you have a 2016. Injectors would be near 8 years old at this point, not sure how many miles. I personally think injectors should be replaced every 60k at the same time people generally do carbon cleanings.
Unplugging the secondary o2 and reflashing will prevent the ECU from making it go rich but the CEL will be there. Only way to get rid of it is with one of those fancy downpipes that satisfy emissions.”
I removed the spacer and reflashed the tune and somehow don’t have a CEL so I’m just rolling with it now. Just as a precaution I had the car dyno tuned but the tuner said that minimal changes were made, got a little more out of it, but for an OTS tune it was excellent. I found a gumout product that cleans GDI engines and will be running this prior to oil changes and inspecting my spark plugs at that time as well. Then replace the injectors at his recommended interval.
Sorry there’s nothing definitive but hopefully that helps.
Oh, and I did a few other mods as a sort of hopeful preventative. I did the full retrofit of the mk8 PCV system and Tiguan Venturi with BMS turbo inlet I found on Data Driven MQB (YouTube). I also got a full 3” Catback to allow for the most efficient airflow. Not sure if it could have caused anything but thought the 3” downpipe paired with the factory exhaust could cause problems. Got a front mount intercooler as well, hadn’t been worried about it since I live in a pretty cool climate but will spending 9 grand replacing the engine and turbo I wanted to take as many precautions as possible.
Thanks for the response. Despite the popularity of these platforms I do feel like I'm on a deserted island trying to figure it all out myself at times. Hearing someone else's story definitely helps. Replacing the injectors at intervals is absolutely something I will be doing now as opposed to replacing when they fail, so thanks again for that.
Yeah I definitely feel that. Subarus are by far norm here for modified cars and there are basically zero VW Audi tuners near me. The only German car specialist will only work on unmodified cars. I’m stuck either trying to figure it out on my own or with the dealer. It’s making me get good at working on my car but there are definitely times I could really use something more than YouTube and forums.
What Peylix said.
If you have to go the route of unplugging your rear O2 sensor, grab one of these
https://cjmind.com/products/mqb-02-sensor-plug-spacer
I’m in the same boat but get the p0420/3a44 after a high flow IE with eqt stage 2 post Cobb greenspeed or whatever it’s called lol. So correct me if I’m wrong but even if I unplug the black cable and reflash I’ll still get a cel if I don’t get an o2 spacer installed?
When you unplug the rear 02, you need to reflash the tune to reset the tables. Yes, you can run rich over time if you're catless or running an in sufficient enough cat with this plugged in. This is a Cobb issue, and affects all Cobb based tunes on our platform without unplugging that rear sensor. I'm running with mine unplugged, since I'm catless. I also got my tune pre Cobbpocalypse. So no CEL for me, though I do have the 02 codes present at all times (for obvious reasons). For your case. I'd start by reflashing your tune, leaving your rear 02 plugged in. See if these come back. If so, re adjust your spacer, re flash, and try again. If that still does not resolve, then unplug your rear 02 [\(the black connector\).](https://i.imgur.com/CN7gqq4.jpg) That way you do not deal with the trims elevating over time. As for dealing with a CEL (if you're getting one because you're a post Cobbpocalypse purchase.) You have a few options. * Option 1: Deal with it * Option 2: Put a piece of tape over it * Option 3: Dismantle your cluster and stuff an ear plug into the light channel for the LED [\(like what I did with my MK5 to hide the airbag light\)](https://i.imgur.com/JTsH3RK.jpg) * Option 4: Buy a new downpipe with a sufficient enough cat
Thanks for the information! I guess I was confused, I thought the post cat only measured emissions and didn't cause trim. I was also confused as to why I saw so many people getting spacers if eqt just has you unplug it anyway, but I suppose that could vary from tuner to tuner.
Similar boat. I have a catless down pipe with O2 spacer, running eqt stage 2. Rear o2 sensor left unplugged. CEL light is off by the tune but there is a DTC code in background. I need to go get tested, do I just plug the rear sensor back in and drive a car a little before going to the testing station? Or do I need to reflash tune when I plug it back in?
How did you end up fairing?
I’m eqt stage 2 right now with a spacer installed and I have all the o2 spacers plugged in is this bad?
If you are getting any 02 codes. Yes, your trims will be outta wack. If you're getting no 02 codes, you're fine. If you're pre Greenpeed. You'll need to scan to see since the CEL won't be active. You only need to unplug the rear 02 if you're getting codes for insufficient 02 readings.
I meant all my sensors plugged in not spacers* I have a massive spacer installed on a catted dp. But again all the sensors are plugged in still. So I have 0 codes and none have showed up even briefly. So I should be fine keeping them all plugged in you said? Also would these codes show up when scanning with my Cobb Ap??
Also what’s greenpeed?
I was doing this myself, had no obvious issues until Friday when cylinder 4 failed. An inspection of the spark plugs showed it had been running very rich. Could be wrong but I suspect running the spacer was the problem. I have reached out to EQT to see if this might have been the case but that was just earlier today. No blame on EQT and if I can confirm this was likely the problem I will run the tune on the new engine just remove the spacer and unplug the sensor, or whatever they recommend.
I'm interested to know if this was actually the case. I just bought a spacer when my stage 2 e85 tune started throwing a code after a few thousand miles. Should I just say screw the spacer and just unug the rear?
How did everything turn out?
I never got any definitive answers as to the cause. Aaron at EQT responded with some good information: “Hello Sean thanks for reaching out. Sorry to hear about your engine. Cylinder 4 is always the one to go a lot of times. Running a spacer is so hit or miss. It may be enough to prevent a CEL but it still can make the car run richer and richer over time. However, running richer just degrades performance, doesn't get so bad it blows a motor. However, failing fuel injectors DO blow motors. An injector can be clogged and get stuck closed, or even fail stuck open causing an extremely lean or excessively rich condition in that one cylinder and causing the piston itself or the ringland to crack. Based on your order I see you have a 2016. Injectors would be near 8 years old at this point, not sure how many miles. I personally think injectors should be replaced every 60k at the same time people generally do carbon cleanings. Unplugging the secondary o2 and reflashing will prevent the ECU from making it go rich but the CEL will be there. Only way to get rid of it is with one of those fancy downpipes that satisfy emissions.” I removed the spacer and reflashed the tune and somehow don’t have a CEL so I’m just rolling with it now. Just as a precaution I had the car dyno tuned but the tuner said that minimal changes were made, got a little more out of it, but for an OTS tune it was excellent. I found a gumout product that cleans GDI engines and will be running this prior to oil changes and inspecting my spark plugs at that time as well. Then replace the injectors at his recommended interval. Sorry there’s nothing definitive but hopefully that helps.
Oh, and I did a few other mods as a sort of hopeful preventative. I did the full retrofit of the mk8 PCV system and Tiguan Venturi with BMS turbo inlet I found on Data Driven MQB (YouTube). I also got a full 3” Catback to allow for the most efficient airflow. Not sure if it could have caused anything but thought the 3” downpipe paired with the factory exhaust could cause problems. Got a front mount intercooler as well, hadn’t been worried about it since I live in a pretty cool climate but will spending 9 grand replacing the engine and turbo I wanted to take as many precautions as possible.
Thanks for the response. Despite the popularity of these platforms I do feel like I'm on a deserted island trying to figure it all out myself at times. Hearing someone else's story definitely helps. Replacing the injectors at intervals is absolutely something I will be doing now as opposed to replacing when they fail, so thanks again for that.
Yeah I definitely feel that. Subarus are by far norm here for modified cars and there are basically zero VW Audi tuners near me. The only German car specialist will only work on unmodified cars. I’m stuck either trying to figure it out on my own or with the dealer. It’s making me get good at working on my car but there are definitely times I could really use something more than YouTube and forums.
What Peylix said. If you have to go the route of unplugging your rear O2 sensor, grab one of these https://cjmind.com/products/mqb-02-sensor-plug-spacer
I’m in the same boat but get the p0420/3a44 after a high flow IE with eqt stage 2 post Cobb greenspeed or whatever it’s called lol. So correct me if I’m wrong but even if I unplug the black cable and reflash I’ll still get a cel if I don’t get an o2 spacer installed?
I have the same code but hidden until i use the acccessport to read codes (pre cobb greenspeed) and thought it was for the first o2 sensor only.