PDA

View Full Version : Question Tried almost everything, need ideas P0421 ?



Jaddi01
02-04-2011, 07:18 PM
Hi Guys,

I'm getting a P0421..

16805 - Warm Up Catalyst: Bank 1: Efficiency Below Threshold
P0421 - 002 - Lower Limit Exceeded

Along with..

16698 - Misfire(s) Detected: Single (unspecified) Cylinder
P0314 - 001 - Upper Limit Exceeded - Intermittent

Now initially I did change the plugs and can't be sure, but this may have been connected to the misfire issue. I realise the misfire can cause the other CAT error but I think it's a little bit more complex than this.

I just put the old plugs back in and will have to see if the misfire error re-appears.

OK, so far using VAG-COM the CAT shows "CAT not OK" when going through the readiness tests. O2 sensors check out fine. Just to be sure I've changed the pre-CAT O2 and will change the post CAT O2 tomorrow.

As of now VAG-COM still reports "CAT not OK" and will still throw P421.

Car also has as of yesterday the new uprated coil packs fitted.

Also did an emissions check on the CAT and it shows everything OK. In fact too good to be true, as I emit (or better said, the car) almost no CO2. So the CAT is working and will pass MOT.

So with only the rear O2 left to change tomorrow, I thought I'd ask if any of you have any professional ideas as to what else it can be if the rear O2 change doesn't do it?

All I can think of is a leak between the CAT and the manifold, but again, nothing apparent...

Any ideas?

John


Audi 2003 2.0 FSI (non-turbo) AWA

yaman
02-04-2011, 07:30 PM
Is the car misfiring, or is it just throwing codes?

Are you clearing the codes, and logging when they
reappear?

Regards
Jim

Jaddi01
02-04-2011, 07:36 PM
Hi yaman.

no obvious misfires at all. Must be so slight I never notice.

I do clear the codes and wait for readiness on all systems before re-checking. I keep a record of the codes when I change a part/sensor to see if there is an pattern.

A4 Lad
02-04-2011, 07:44 PM
Dont quote me on it but the "Cat Not Ok" in the rediness does not actually mean the cat is not working. I would suggest that you get the attention of A8Tech for this one as he is an absolute guru in this field.

Jaddi01
02-04-2011, 08:07 PM
Long time no see A4 Lad... Sounds like a plan, is there some kind of bat signal for him lol?

A4 Lad
02-04-2011, 08:43 PM
lol, very good :)
Just look at the vagcom screen like you are confused and he will sense your woes and swoop in. Or message him :)

a8 tech
03-04-2011, 04:25 PM
First things first
Lets start with the basics

You say you have checked co but what about hc (misfire)

carry out a compression test and cylinder leakage

also try and check inlet manifold vacuum as this may assist with determining if the cat is blocked

If you have a random misfire not cylinder specific then it could well be a blockage on the cat.

I will need to check if you have the nox cat fitted as well but all in good time

tip if there is a misfire then after a period the ecu will switch the injector off on the most counted misfire cylinder so your co will drop down to near normal (red herring indeed)

I'm trying to stay off this forum at present but will try to help unless the thread is hijacked by sarcastic nob jockeys lol

Jaddi01
03-04-2011, 04:46 PM
Thanks for the info. I ran out of time to change the rear O2 today, but I guess it won't make any difference anyhoo.

I do have a Nox CAT fitted and replaced the sensor a few months ago and all seems OK there (unless that temp. sensor has something to do with it.)

I don't currently have access to compression/leakage test equipment, I'll have to ask around. As for inlet vaccum... I had a collapsed pipe going into the oil crank valve which I replaced. I did notice the sucktion was quite high collapsing the pipe onto itself. It wasn't an original corrigated plastic pipe, it was a rubber breather hose someone had fitted at some point. I now have the solid corrigated plastic back on there.

Could this extreme sucktion be a sign that the CAT may be blocked? If so, I (in good scouts tradition) have a spare (used) cat travelling with me in the boot of the cat complete with manifold... just in case :)

a8 tech
03-04-2011, 05:03 PM
The nox cat can also collapse try banging it with your hand to see if rattles


this may help
http://www.aa1car.com/library/exhaust_backpressure.htm

hopefully this will help you narrow down if there is a mechanical fault either with internal combustion leakage or blockages

once you establish the engine and cats are ok then you can start to look in other areas


My rule of thumb is compare with another vehicle if available and if in doubt and you have a spare cat then swap it over

good luck

Jaddi01
03-04-2011, 08:28 PM
By the way that's one hell of a good link you posted! Ta very much. Even though the thought of having a compression problem/leak scares the be-jeez out of me!

Jaddi01
04-04-2011, 06:35 PM
Massive sinking feeling as I've just realised the spare CAT I have won't fit as it's got no EGR!!! Damn it!

Jaddi01
12-04-2011, 08:03 PM
OK just replaced the rear O2... no change.

Did block 47 VAG COM CAT readiness test again.. However noticed the CAT value before starting the test was 0.44. So, that is great as it's below 0.5 the pass mark, i,e, CAT working).

After test completion value is 0.7 - 0.8 and failed. Disconnected the purge valve and the value goes back down to 0.44 but will not start the test as it has then logged a purge valve fault.

I still haven't been able to test for backpressure etc. as asll my mechie mates are either on holiday or choc-a-block with work.

Could this be a purge valve fault? Or maybe the intake solenoid valve (vac lines seem OK)??

Jaddi01
15-04-2011, 01:45 PM
Well I think I've found the problem.

Started the car up this morning and it sounded like a bag of nails. Like the the exhaust was blowing from the engine compartment.

Had a quick look and the EGR pipe from the exhaust to the valve has disconnected itself somewhere in between.

There must be a connection half way along the pipe that has failed. Anyone confirm there is a connection there?

This, as ever is excellent timing as I'm off the Germany on Tuesday. Plus it's again in an area of the engine that only superman could get to.