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Fault Code: 16805....P0421-001

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volkswagendude

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Discussion starter · #1 ·
Address 01: Engine Labels: 077-907-560-AXQ.lbl
Part No SW: 4D0 907 560 DB HW: 8E0 907 560
Component: 4.2L V8/5V G 0010
Revision: 00000000 Serial number: VWZ3Z0D7284659
Coding: 0007875
Shop #: WSC 31414 000 00000

1 Fault Found:
16805 - Warm Up Catalyst; Bank 1: Efficiency Below Threshold
P0421 - 001 - Upper Limit Exceeded - MIL ON
Readiness: 0000 0100


Engine runs fine, no hesitation, no vibration, smooth as silk. What gives?
CEL light just came on tonight for the first time on the way home from work, actually a few seconds right after I started the Touareg to be exact. Last VAG-COM scan was about two weeks ago, no codes stored.



 
Discussion starter · #3 ·
Well 2 days later, the CEL hasn't returned which is very good news.
I'm going to go try and find that cat readiness test on the VAG-COM that you mentioned dvmis. Before I do, is there any proper procedure to do this? Must the engine be at normal operating temperature, cold, or it doesn't matter?



 
Discussion starter · #5 ·
wvicary said:
The cats have to be at the correct temp or the test won't start. Just follow the on screen instructions.
Click to expand...
Thanks!

I did this tonight. This is very time consuming! Something like 20 something steps that need to be completed!?! :eek:

Well I tried anyways. Around the 17th-19th step, give or take, two of those tests refused to work, meaning it always wrote "test off." Test would come on for about 10 secinds and then go off again :confused: I got so frustrated, that I'll try it with a fresh mind tomorrow again.

The important thing is 5 days going now, and no CEL light. Yet.



 
Discussion starter · #7 ·
BonesNTX said:
Hey VWDude,
How many miles have you done in the 5 days?

As you probably know mine kicks the code at about 100 miles...(Well used to CEL after about 100 miles).
Click to expand...
Haven't driven that much this week...I'd estimate close to but not over 100 miles. Now that you wrote this, I'll take it for a good 30 minute high speed spin on the highway, and see what happens.



 
Discussion starter · #8 ·
BonesNTX said:
Hey VWDude,
How many miles have you done in the 5 days?

As you probably know mine kicks the code at about 100 miles...(Well used to CEL after about 100 miles).
Click to expand...
Sorry, forgot to update.
Well its been a good 200 miles I'd say now. In fact, earlier tonight I did a 200km round trip to my brothers. Poured some fuel system cleaner two days ago, kicked it on that trip.

No CEL light yet!



 
Discussion starter · #9 ·
dvmis said:
Clear the codes or run the readiness test of the cats, which they will probably pass. If they return the dealer should change them.
Click to expand...
Two weeks and about 800km later, CEL light came back today. Time for the recall to be performed. Will call them Monday for an appointment.



 
Discussion starter · #11 ·
BonesNTX said:
Dang!

Sorry to hear it lingers on.

FYI...I am still clear, running strong.
Click to expand...
Don't be too sorry now, because today when I fired her up, the CEL light was gone :confused2:

I was always under the impression, that once a CEL light was on, for whatever reason, it had to be cleared manually. I guess not!

So it seems my problem is intermittent. :-k In any case, I'm scheduled for the coil pack replacement for next Tuesday at the dealer.



 
Discussion starter · #12 ·
I really have to update this thread, things have "happened" in the last two days.

Ok, recall was performed on Tuesday as scheduled. I noticed no differences in engines characteristics, like idle smoothness, more power, whatever after the new coils were installed. Gas mileage is an other story perhaps, but too soon to tell, but not the topic here. I never had any running issues to begin with, except for that occasional CEL code(the topic).

Coming to tonight. It came back on :mad:

So I did that "readiness" test with the VAG-COM. The beginning parts were all good news. Oxygen sensors also passed. Now to the bad news. STEP# 13. Bank 1 CAT B1 NOT OK. Cats in Banks 2 passed BTW. Fuel mixture diagnostic in Bank 1 could not be read, due to CEL now having been stored with all that idling to reach this point of stage in the readiness test :mad:
Basically, many steps after #13 could not be performed, due to this CAT B1 not being OK.

Final verdict based on that test. Everything passed, except for the cat.

So what the hell do I do now? Do I ditch the CATS :confused: Which CATS are the B1 ones? As I wrote before, it seems that the B2 ones are passing the test.



 
#14 ·
Good idea... the CAT's are only as good as the sensor says so. By the way, aren't the catalytics under the emmision equipment warranty?
 
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Discussion starter · #15 ·
siberian said:
Are you sure it's not the O2 sensors on the cats?

siberian
Click to expand...
Not sure....but do me a favour, go try out the "readiness" test on the VAG-COM, and tell me what you see in Step #13. It is that step only that I seem to fail in, and where I get the message in field four, "CAT B1 Not Ok."

In all the oxygen tests, it passes, if my interpretations of the VAG-COM are even correct.

I don't know....


TVaitonis said:
Good idea... the CAT's are only as good as the sensor says so. By the way, aren't the catalytics under the emmision equipment warranty?
Click to expand...
Makes sense, I thought the same, but why does the readiness test have a separate cat test from the oxygen sensors test?

My Touareg is now at 144700km. I think that I long passed that emissions warranty unfortunately. Was it not 8 years/128000km or something like that?



 
#16 ·
Well, I haven't had the joy of dealing with emission faults on the Touareg but a couple years ago I was having an issue with one of my Pathfinders where the codes indicated an O2 problem. What I learned then was that Nissan used a pre-heating O2 so it would be more accurate before the exhaust reached full temperature. This is a guess..... but that may explain the test for O2 function and the test of the CAT for efficiency as two different things. Hope this helps a little bit.
 
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#17 ·
VW Dude....Just remembered a chain of events with my Land Rover last fall. Got an intermittant CEL and when scanned it showed a CAT fault. You know what it really was? MAF sensor. Was messing up the mixture just enough to throw a code. Few thousand miles and CEL free.
 
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Discussion starter · #18 ·
^^^^^^Hmmm.....do you think that I should use some MAF cleaner then? You know, that spray stuff, that cleans but leaves no residue behind. Usually isopropyl alcohol based.


A little something from Ross Tech, but still not conclusive. So what does "replace warm up catalyst bank 1 mean?" :confused: What do I replace, with out having to resort to the replace everything one by one until problem is found? I'll be slightly pissed if I change out the oxygen sensors, only to find out later that it made no difference because my cat was fried anyways. Need_more_input on hypothesis, to embark on actual procedure with hopeful conclusion.

BTW, since the Touareg is easy to crawl under, especially on xtra mode, I'd like this to be DIY repair.

16805/P0421/001057 - Warm Up Catalyst; Bank 1: Efficiency Below Threshold
Possible Causes
Warm Up Catalyst Bank 1 faulty
Possible Solutions
Check Warm Up Catalyst Bank 1
Set Readiness
Replace Warm Up Catalyst Bank 1



 
#19 ·
VW Dude, my doing it won't help as I have a 2008 and it's a V6 not a V8 so whatever messages I may get from the readiness will probably not be what you need for your set-up.

siberian
 
#20 ·
Let's work through this logically. The message you get is:

16805 - Warm Up Catalyst; Bank 1: Efficiency Below Threshold

This means that the difference between the pre cat O2 sensor and post cat O2 sensor is greater than normal. Otherwise it would signal Efficiency Below Threshold INTERMITTENT meaning in this case that there is a difference between them but not enough to affect the cat output. A warning if you like, and things to check then would be like manifold leaks etc.

It is a bit early to think that your cat is toast and even if it were you'd feel it as your car would turn to mush accelerating. Thus assuming that it isn't doing that, it would point to the O2.

I would change the pre-cat O2 because it says warm up, clear the codes from the computer and see whether it appears again after running it about 200 miles (some take that long to show up). If that doesn't work, change out the post cat O2, clear the code and try again and that IMHO should do it. In the worst case that it doesn't, it's still cheaper than replacing the entire cat - which btw should still be under warranty.

HTH

siberian
 
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