[1.6 FSI P0420] - No EML

Cheers @rotifer II. I have precluded the sensors being faulty because they are practically new.

I do get a rattle from the ageing exhaust though and the flanges, seals have definitely seen better days.

I haven't figured out whether the converters available online are suitable or not.
 
The "Catalyst Below Efficiency"refers to the front cat, as the rear NOx cat has, in the FSI, it's own set of fault conditions, and DTCs.

P0420 is triggered, because the lambda in the rear cat, is indicating a higher level of CO than is expected.
Because there is no EML, the problem is not causing high emissions at the tailpipe. I'm guessing it a minor, or transitory condition. Probably the consequence of something else, rather than a fault. Not the cat, is my guess.
I'd start with taking the readings of the two lambdas, as a log, and, hopefully, get an idea of what's going on.

If there was an EML, or the emissions were high, (at MoT for example), my question would be:
Are there actually high residual CO levels in the exhaust, or are the readings from the rear lambda incorrect?

If the CO levels actually are high, then it is because either the cat is not working effectively, (to reduce the CO), or the mixture is too rich, producing levels of CO which the cat can't deal with.
If it's a mixture problem, the front lambda readings should, (I think), show that. With a lambda of less than 1.0.
If the cat is not working effectively, the front lambda readings will show normal operation, (lambda of more than 1.0, typically 1.5 to 3.0, depending on engine being in Stratified, or Homogenous Mode), but the rear lambda will be greater than 1.0, indicating high CO.
Warning: The above is based on my current understanding, and may not be correct.
Mac.
 
OK here are some more diagnostics that I have done today. I was trying to chase down the P0420 code, nut no EML at all and no misfires whatsoever.

I noticed that when the car is warmed up adequately after a 30' trip, and then left idling, you can notice that the engine is alternating between two states, a normal idle and higher pitched idle (you could also say rough idle but rpm is stable-ish). Happens every 3-4 minutes or so. I plugged the diagnostics in and I get the following (in chronological order):

IMG_20250112_192744.jpg


IMG_20250112_192844.jpg

IMG_20250112_192846.jpg

IMG_20250112_192847.jpg


Fuel trims look like this:

IMG_20250112_193738.jpg


It appears that the purge valve has something to do with it. The engine does not misfire as I know how it sounds/feels like.

Evros
 
If you get the chance log 070, 031, (Lambda Setpoint and Actual, to see what effect on lambda the tank vent flow is having), and 007, (check for SV in Block 4).
Mac.
 
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Thanks Mac.

Just tried but it has cooled down. It has to get warmed up all the way for this to happen.

As it is now after having sat for 15 minutes; the vent will open/close without the readiness bit #4 to flip and the misfire detection is always enabled. Group 31 is bang on 1.00 on both fields.

So this must have something to do with temperature, either coolant or cat. Leaning more towards cat (pun).

Any idea which block monitors the post cat lambda? The label file is confusing me a great deal.
 
Evripidis said:
Thanks Mac.

Just tried but it has cooled down. It has to get warmed up all the way for this to happen.

As it is now after having sat for 15 minutes; the vent will open/close without the readiness bit #4 to flip and the misfire detection is always enabled. Group 31 is bang on 1.00 on both fields.

So this must have something to do with temperature, either coolant or cat. Leaning more towards cat (pun).

Any idea which block monitors the post cat lambda? The label file is confusing me a great deal.
Click to expand...
It does seem to be running at a higher temperature than I've seen elsewhere. The mechanical thermostat should be open at 110C, and the electronically controlled thermostat, at between 90.0- 105.0C.
I think Lambda 2 is 036.
Mac.
 
Evripidis said:
So it could be running lean.
Click to expand...

It shouldn't get that hot, regardless of what engine running condition is. The mechanical 'stat should have opened around 110, and the ECU controlled 'stat should have opened a bit before that.
I think there's a problem, not sure what, but it suggests the cooing system isn't cooling very well.
But, and it's a big but, the one reading of 118C is just that, just one reading. The only way to find out if that one reading means anything is a log.
Mac.
 
Evripidis said:
I'll try another session when I can.
Click to expand...
Looking at the logs I have, 113C is the maximum I can find.
The normal range is 108 - 111C. Typically the temperature range is small. The ECU's control of the proportional thermostat sees to that. So seeing 118C worried me.
Most of the logs are from my FSI'zy.
Mac.
 
I ve take the precat section of the exhaust out to have a look. It was indeed leaking.

I replaced two out of the three gaskets, cold not find a replacement for the third. Some welding and then put it back. I used some paste in the process.

When I took the readings it was after a 20 mile trip and the car was idling for a good 15 minutes. Maybe this is why I am seeing the occasional 118 degrees.

The cooling system is brand new all through. I only reused some hoses. Cap, tank, radiator, complete thermostat, pipe, etc.

The engine came from a forum breaker but its pedigree is questionable.
 
OK, after all the exhaust work, I still get the P0420 (no EML).

I drove for about 1 hour and maybe 60km in all conditions and when I reached home I plugged in vcds.

It makes no difference if the error codes are cleared or not. The same alternating pitch happens.

I have taken notice of groups 7, 70 and 31 and here are some results:

IMG_20250113_191903[1].jpg

IMG_20250113_191907[1].jpg


So in effect when the purge valve is open the ecu is in stratified mode and when it is closed it is in homogeneous mode.

This makes sense as to the pitch that the engine makes.

So the question is; is this normal or not and if it is, do I need a new evap purge valve?

Evros
 
Hi Mac,

No reason it wouldn't. This is just what I am observing with my realisation of this experiment. Also I cannot do any drive tests to see what is the case while on the move. Only idling.

What I am guessing is that maybe the valve is not opening or closing in a calibrated manner, e.g., it is instructed to do 30% but it is not. No real way of knowing I guess.

Evros
 
Evripidis said:
Hi Mac,

No reason it wouldn't. This is just what I am observing with my realisation of this experiment. Also I cannot do any drive tests to see what is the case while on the move. Only idling.

What I am guessing is that maybe the valve is not opening or closing in a calibrated manner, e.g., it is instructed to do 30% but it is not. No real way of knowing I guess.

Evros
Click to expand...
First run adaptation on the Tank Vent System. I'm guessing you are using the original ECU, but the "new" N80 valve is not the one that was adapted to it.
Mac.
Edit: If the N80 is faulty, or the EVAP circuit is restricted, the adaptation will fail.
 
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