P0420 Nightmare

[DuckyDok]

Hello,
5-6 months ago I've sent the turbo to be repaired,the Wastegate was very bad.
I've installed the turbo after I got it back,and after 200-3000km I've had a Check Engine with P0420.
( in the same time the car didn't had any stoppage or hesitation when going fast or slow. )
After another 200 300km same error ( after cat cycle ).
Last week I did some leak test,but there wasn't a single leak.
On vcds the cat test PASSED(VCDS Readiness)everytime,but the temperature doesn't rise more than 300 or so.

I don't thing that the cat is dead,maybe there is something else,because the car runs great,no smoke or bad smell.

Does someone has any idea?

[Smac770]

We've discussed the process by which the ECM trips P0420 before: https://www.audizine.com/forum/showt...1#post14500925
I don't know what the cat test passed means. But P0420 is a result of the test done each drive cycle. Could be the cat emissions readiness is set, but still have a P0420 event occur, I suppose.
As you can see from the logged parameters, the cat test is dependent on the lambda and jump sensors (the pre-cat and post-cat O2 sensors) working correctly. Replacing them to see if there's a change is probably cheaper than just jumping into a cat replacement.

[marshallnoise]

I believe that low oil pressure conditions off idle can cause this code too because the cam doesn't get advanced quickly enough. If the injectors are putting more fuel in and the ECM is commanding camshaft advance and the car can't deliver, it would dump extra fuel into the exhaust. But I would definitely go through the usual things first.

[Smac770]

Yeah, but if the VVT management is that slow, he'll have some P034x code.

[marshallnoise]

Yeah, but if the VVT management is that slow, he'll have some P034x code.

Good point.

[DuckyDok]

So i have new injectors for a long time,maybe 1 year and 8 months,new HPFP+tapper,just made the Timing like 2 months ago,and turbo before timing.
The problem was after the Turbo was installed,like I said above,the Error comes and after another 300km goes,then another 300-400km or so, after it does his cicyle,then appears back,and so on.
I've been told by a Tehnician from VW that that's the cat,but I don't belive it to be directly after the turbo change.
[ P.S when i've changed the turbo I didn't got out the sensor,only disconnect it ]

List of changed things on motor side:
PCV assembly+hoses, HPFP Hitachi+tapper, Turbo IHI repaired,Injectors Bosch,Timing Assembly+Oil Pump chain,GFB DV+, and some other things that i've forgot but those are not so important.

Should I check the Parameters from the link metioned by Smac770,or should i just change the o2's?

[Smac770]

It's like it's tripping once, then self clearing, then coming back once, etc. Some DTCs will reset on ignition off, some will reset on a next success, some don't reset until a streak of success. This can be seen in the DTC info. For example, my P0420 is from August, with 29 faults since. Currently, the unlearning counter is at 21. So it's reported as an intermittent - confirmed DTC. It could well be my cat is marginal, but I can clear codes, drive easy to get readiness set, pass emissions, then ignore it for another year. At 15 years old, I'm sure it's the cat. But I'm not replacing it till push comes to shove.

In your case, it could simply be because the turbo is fixed and now exposing a different operating scenario whereby the test is failing. But without a log to see what's going on with what, that's all speculation. If you just want to go parts cannon, if there's no exhaust leak, then replace 02s, if no joy, replace cat.

[DuckyDok]

Hi again,
Did a Log,idk if this is good or not,i just took the info from that post and search it through VCDS.
First log is at 110km 90' : https://datazap.me/u/chrissx/log-171...8?log=0&data=0
Sec. is at 85km after the B1S1 OK : [ same link but press the "reload" buton next to the file name ]

This screenshot is after 40 min of driving,the Oxygen Sensor Heating Failed.
link if not working : https://imgur.com/a/bPNJOpj

[DuckyDok]

So someone has any info or something?

[marshallnoise]

That last image you posted sure makes it look like a bad primary O2 sensor.

[Smac770]

You didn't do Group UDS, so the samples are all done sequentially, only one value per interval, not in a single group with all values per interval. So that's going to make the curves a lot less accurate.

By time you do the log, the cat test has already run and passed, according to the values: test result: CatB1 Ok / test value: 1.3281. The other log has a really high value and Test Off. Keep in mind that the XLS log for when I created that chart has 8600 records, with all 8 parameters sampled 7 times second, covering 20 minutes. The logs from the site don't even show a single throttle release to confirm the jump sensor goes to 0 under that condition.

Exhaust temp is pretty useless. There's no actual sensors on the engine. That's nothing but a modeled value based on the air mass consumed since start.

It appears your cat test is passing fine. But that heater failure. So you really have no DTCs from 01-engine? This is a CDNC engine?

If you go into Mode 6, what is the monitor id 65 ($41) value? 65 value should reflect the 133 ($85) test. Looks like P0135 should get set if the temp is still under 715°C after 40 seconds. And the 66 ($42) value should reflect the 129 ($81) test, which is for the resistance of the internal cell, and should set P0141 if failed. If you go into Mode 8, can you invoke either of these tests manually?

That it's related to the turbo swap, yeah, probably something got trashed about the sensors or their cables. But which one is the problem is not clear without actual error codes. That you're not getting error codes seems really odd. So just replace both sensors and see where it goes.

[DuckyDok]

The only problem I have it's with the P2261,like I specified I have a GFB DV+,so I think that comes from there. No other problems. I will buy the both of them from Bosch.

And kudos for the explanation 👏
This is a CDNC engine( 08.2011 )

[JLAllroad]

The only problem I have it's with the P2261,like I specified I have a GFB DV+,so I think that comes from there. No other problems. I will buy the both of them from Bosch.

And kudos for the explanation
This is a CDNC engine( 08.2011 )

You wouldn’t get that code from a GFB DV+ as it uses the OE actuator/electronics


Sent from my iPhone using Audizine Forum

[Smac770]

There's no documentation of exactly how the P2261 is computed, so there's no way to know if it's related to the electrical operation of the N249 solenoid, or based on the pressure changes that should be seen when it's activated. Or maybe either, with different subcodes.

[DuckyDok]

Update
I’ve changed both of O2,the problem still persists.

Like a said before,there is no holding back,no power loss,no rotten eggs smell, or anything that would indicate that the cat is dead.
Both old O2 were black.

This appeared after changing the Turbo.

And I have 2 small holes in the exhaust,one after the flex pipe where the silencer is,and the second one is on the Final silencer.
I dont think can be the problem.

[old guy]

A hole fairly close (but downstream) from the rear O2 sensor can cause a P0420. It happened to me on my B6 1.8T. Easy enough to eliminate. Get a tube of muffler putty or a roll of muffler wrap, plug the hole, and see if it helps.

[DuckyDok]

Maybe last Update:
After changing the upper O2 ,and resetting the readings with VCDS,i still got the same code.

But now over 500 or more km it’s not appearing anymore,the car acceleration is more powerful,and the car runs fine.

I don’t know why my ECU didn’t reset when i did the factory reset,and adaptation. I still had to delete the Code for like 2 times after.

If it appears again,i will get another exhaust. But I don’t think its gonna appear.

Strate that the O2 didn’t appear defect on vcds.

Thanks to everyone for help.

[DuckyDok]

Update again:

So I changed the 2 O2 sensors,put muffler putty with muffler wrap and even did MIG Soldering on the holes.

The Check engine still comes on.

I don't know what else to fix.. Maybe the Turbo wasn't repaired good or there is a leak somewhere that I can't find??

This car only makes me problem,can't sell it now because i've changed over 5000 Euros in parts.

[ Like I've said before, the problem came directly after i've put the turbo on ]

[PrestineAuto]

The proper way to diagnose a vehicle with a p0420 code is by watching the live data on both sensors while driving on a highway, and at idle. The sensors should NOT have matching voltages or switching between rich and lean 0.9 volts- 0.1 volts. The secondary O2 sensor should not be switching at the same time as the front O2. It should stay pretty static while going 60 mph. Watching the voltages on a graph style scale should give you a better understanding. You’ll need a real scan tool for that. If the rear O2 sensor is matching the front O2 sensor, then that means the catalytic converter is not operating efficiently and WILL cause a p0420 code depending on the operating conditions. For example, on my ford transit connect that I bought, I drove all highway to my home and got no codes during that drive. But when I do city driving, the code comes back. The converter can operate properly when highway driving because it has a better time heating up and technically works better than the city driving style. You must monitor the live data for both O2 sensors to properly diagnose. I’m sure your converter is bad. If you just wanna pass emissions, put a spacer on the rear O2 sensor, it’ll fool the computer into thinking the catalytic converter works just fine because it’s seeing a different oxygen rating than the front O2. Works every time.

[Smac770]

There's no voltage for a wideband lambda sensor. The ECM can fabricate a pseudo-voltage value, but it has no relation to the voltage of a jump sensor. So trying to compare the "voltage" of the front and rear sensors is meaningless. You compare the correct values independently against known good expectations. Or better yet, understand exactly why the code trips, and then eval exactly that input data.


"The Check engine still comes on."
That's not a code(s). What is the real information behind the MIL being on? Ie, the complete text of the 01-engine section of the VCDS autoscan log, at a minimum.

[DuckyDok]

This are the engine codes.

Address 01: Engine Labels: 06H-907-115-CAB.clb
Control Module Part Number: 8K2 907 115 AE HW: 8K2 907 115 L
Component and/or Version: 2.0l R4/4V TF H09 0002
Software Coding: 0104000C18470160
Work Shop Code: WSC 06324 000 00000
ASAM Dataset: EV_ECM20TFS0118K2907115AE 001003 (AU48)
ROD: EV_ECM20TFS0118K2907115AE.rod
VCID: 72EB6FCFA5AF281615-8026
2 Faults Found:

2886 - Catalyst System; Bank 1
P0420 00 [237] - Efficiency Below Threshold
MIL ON - Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 2
Fault Frequency: 1
Mileage: 198259 km
Date: 2025.02.15
Time: 19:05:40

Engine speed: 1691.50 /min
Normed load value: 16.1 %
Vehicle speed: 63 km/h
Coolant temperature: 96 °C
Intake air temperature: 12 °C
Ambient air pressure: 960 mbar
Voltage terminal 30: 14.512 V
Unlearning counter according OBD: 40

7663 - Boost Pressure Control Valve (N249)
P2261 00 [096] - Mechanical Malfunction
Intermittent - Not Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 2
Fault Frequency: 1
Mileage: 198387 km
Date: 2025.02.20
Time: 09:17:27

Engine speed: 1333.50 /min
Normed load value: 5.9 %
Vehicle speed: 70 km/h
Coolant temperature: 87 °C
Intake air temperature: 3 °C
Ambient air pressure: 960 mbar
Voltage terminal 30: 14.630 V
Unlearning counter according OBD: 40


Readiness: 0000 0000


Funny thing is that i'm working in a Mercedes Dealership,but no one wants to help me find the problem because they "don't know" and don't wanna work on "Audi".

[Smac770]

Ok, so the two codes are direct. The P2261 one, you still have that non-stock recirc valve installed? You'll need to take up that code with GFB; it's not a "stock issue" that we can evaluate against a normal car.

And then the P0420, I see no reason to relate it to the P2261 fault. So standalone issue. So start with logging and capture the event of the cat test, as I did here: https://www.audizine.com/forum/showt...1#post14500925
You did a log before, but it lacked necessary things and had unnecessary things. The things I logged for that graph were:

IDE00021 > Engine RPM
IDE00083 > Throttle valve position (absolute)
IDE00559 > pre-cat lambda sensor lambda + current [the lambda is the value you care about, you can dump the current part using Excel]
IDE00560-MAS04121 > post-cat jump sensor voltage
IDE00592 Status of oxygen sensor control > should be closed loop / using O2 sensors, or the fuel trims are not being managed by the lambda at that time
IDE01873 > Test of catalytic converter: measured value
IDE01874 > Test of catalytic converter: result

So for the last two, somewhere along in the log, you'll see it change from 0 / Test off to 0 / Test on and then to X / whatever. For me, whatever is CatB1 Ok, and X is some value like 1.4

The point of the test, which is what trips the P0420, is to eval the cat's OSC (oxygen storage capacity). Anything that's throwing off the assessment of that, such as stray O2 in the space or errant sensors or such, will create a depressed test result.

This is a stock cat?


In that same thread, https://www.audizine.com/forum/showt...1#post14537165 , we see the resolution to the P0420 for wilmar was realizing he had air leaks in the PCV system and fixed them. They were new as he said "car never had P0420 that I know of until I installed the new turbo". So likely the turbo process trashed that metal flex pipe that runs down to the turbo from the PCV. You might need to check yours for no leak and good seal.

[Theiceman]

interesting that last post

as i was quietly thinking .. " i wonder if he got those 4 turbo - cat nuts tight with a new gasket ,, " air leaking in could throw it all off.. if this truly has started since just replacing turbo , i would definitely relook at what was done.

there is also the exhaust manifold gasket to consider , any leaking there ?

[DuckyDok]

Im thinking the same thing like "Theiceman" thinks.
Maybe something got trashed and didn't see it.

I have a new Exhaust Mainfold Gasket,I did a Leak test with smoke machine,but didn't see anything. I will do another one from the exhaust tip all the way up on the exhaust.

The CAT was/its stock and the car runs perfectly fine. [That's why i'm saying that the CAT can't be *dead* ]

One PCV pipe broke,the one that connects the Turbo and the PCV case,it broke when i've got the Turbo out cause the plastic [metal flex pipe] didn't flex at all. and the whole PCV Case was changed too.
Or maybe the last guy who had the car modified the ECU in any way to hide some problems and now after the Turbo Swap the problem start showing?

I will try to do the smoke test one more time and look maybe there is a gasket not staying good or I didn't put it good. And i will look to do a IDE test.

[Smac770]

A lot of smoke machines are low pressure because anything over 1 psi and you're risking the EVAP system; half that is the typical target. But for the exhaust system, if you can crank the pressure up and cap the exhaust outlets, that would be the way to go. Set it to 20 psi and if there's a leak, you'll probably be able to feel it as much as see/hear it. Remove one O2 sensor and put the feed in there, then do the same with the other O2 sensor position, to test on both sides of the cat substrate.

Don't forget there's a torque spec order to the exhaust manifold nuts.
front > mid > rear > mid rear > mid front
all to 5 Nm, then all to 12 Nm, then all to 16 Nm, then all to 25 Nm

Did you loosen any of the four nuts along the lower edge of the manifold, on the two clamp bar? Don't loosen them, but if you did, 30 Nm.

And of course, all those nuts, lower manifold four (if they were loosened), upper manifold five, turbo to cat four, they are all replace if removed.

Also note, that N249 bridges the turbo outlet and turbo inlet, so any leak of that / through that would contribute as well. It wouldn't hurt to go back to a stock recirc unit until you've seen the situation through. Excess variables only complicate things.

[DuckyDok]

https://log.tunezilla.com/s/U9HgO6TR 50km TESTOFF

https://log.tunezilla.com/s/yByRvZFE a little Agressive driving with TESTOFF, 1s after the i've stopped the test then appeared B1 OK

https://log.tunezilla.com/s/KK85x41R IDLE after TEST B1 OK

[ I did another one driving normal with testoff but it got corrupted cause my cable disconnected ]

[RPMtech147]

I didn't read the entire thread, but I didn't see that OP actually replaced the cat with an OE unit.

I've never, ever seen a B8, much less an Audi throw a P0420/430 and it not be a faulty cat. To add insult to injury, the aftermarket replacements are garage. They use a fraction of the substrate and will continue to cause 420 faults. You have to use an actual Audi downpipe/cat or a cat large enough to keep the DME happy unless you tune the fault out.

[DuckyDok]

Cant find any leaks,the Turbo housing screws were loose and that was all.
If the CAT is done then i dont care anymore,too much investment in this car.
Maybe in the summer i will cut the flex pipe and get the cat out to leave it in a solution overnight for it to get unclogged.

Thanks to Smac770 and everyone else for the information and help!

[silver_tt]

The CAT was/its stock and the car runs perfectly fine. [That's why i'm saying that the CAT can't be *dead* ]

This is not a valid assumption. Odds are you need a new catalytic converter. The OE part in the USA is $2,000 ($2,700 with a $700 core charge).

Maybe in the summer i will cut the flex pipe and get the cat out to leave it in a solution overnight for it to get unclogged.

To get the cat out you don't need to cut anything, it's easy to remove with a few bolts. Leaving it in a solution won't fix it.

[marcomarco]

Go to the local Napa or other parts shop and purchase for a few dollars 'spark plug defouler' they come in packs of two. Next source an SOS pad and tear a few strands off. Remove your downstream 02 sensor. Wrap the tip of the sensor with the strands from the SOS pad and screw it into the spark plug defouler that way. Screw the spark plug defouler/02 sensor back into your exhaust as one piece. Boom...no more p0420. Did this to my civic and it's been 7 yrs now no p0420. Make sure the cat isn't actually plugged though. Also the spark plug defouler has a small hole in the tip. Can't remember if I drilled it out slightly to make it a bit larger. There are videos online showing how to do this. Other option... purchase a new OEM cat for $2K.

[DuckyDok]

I've already put the car for sale,it's a money pit.

This car was the worst car i've had in my whole life. A 15 years old car having over 70% of parts changed is totally absurd. I have 2 Golf 5 FSI,they are 20 years old and they run much better and never had so many complicated things like this shit box.
Everyone in my group of friends who has an Audi has problems. Here in Germany they will not fix your "Oil consumption problem",because they wrote in the MANUAL,and the german LAWS ARE STUPID.
Even so, the german car brands are getting worse every year. I think I will go for another brand from another Continent,like Japan. Maybe they are much better than our plastic ones.

[JLAllroad]

Go to the local Napa or other parts shop and purchase for a few dollars 'spark plug defouler' they come in packs of two. Next source an SOS pad and tear a few strands off. Remove your downstream 02 sensor. Wrap the tip of the sensor with the strands from the SOS pad and screw it into the spark plug defouler that way. Screw the spark plug defouler/02 sensor back into your exhaust as one piece. Boom...no more p0420. Did this to my civic and it's been 7 yrs now no p0420. Make sure the cat isn't actually plugged though. Also the spark plug defouler has a small hole in the tip. Can't remember if I drilled it out slightly to make it a bit larger. There are videos online showing how to do this. Other option... purchase a new OEM cat for $2K.

Yeah spacers and “mini cats” rarely work on B8/8.5’s, hence why many tuners just keep the second O2 (catalyst monitor) from reaching readiness and kicking a code.

[Grandmaster]

Will it still pass a state emissions test by doing this?

[silver_tt]

It might depend on the state. In the state I live in they will do a checksum on your ECU and if it doesn't match stock you will fail regardless if readiness is set or not. They use 3rd party software to do this. The only way to get around it that I know of is to flash back to stock before the emissions test; some tunes come with a device you can buy for extra to do this.