Cat issue

thorsy22

Registered User
Been told need to replace a lambda sensor and the cat.

Now followed the instructions from this link http://www.wikitt.org/wikiTT/images/f/fc/TTweakers-Guide.pdf to test the cat and all the lambda/oxygen sensors. But when it comes to testing the cat (basic settings block 46) it just stays on test off. The question is how long does it take for the test to run or anything I need to do to initiate the test?
When checking the readiness this is the only part that hasn't passed so am beginning to think the cat is knackered but I get a reading of 0.13 which would suggest the cat is in good condition according to the link?

Anyone got any other ideas/suggestions £400 is a lot to spend on a part if its not knackered!
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
Which lambda (pre CAT wideband or post CAT) and what fault codes? post CAT lambda is there just to check the CAT is working and is designed to throw a fault code if it the ECU thinks the CAT is not doing what it should (CO goes too high)...

Have you have the CO checked? if its too high then it could be the CAT causing the problem but I have seen (on Welly's car) a disconnected N249 valve cause a similar CO issue... he did have the N112 valve (which the AMK doesn't have) disconnected too but it was playing havoc with idle and fast idle fuelling causing the CO to be read high...

Have you done an N249 bypass at all and disconnected the N249? are there any other fault codes?

<tuffty/>
 

thorsy22

Registered User
Cheers for the rapid response Tuffty.

It was high emissions from an MOT failure, no fault codes that are engine related (the only fault code I have is 1134 iirc which is something to with alarm horn battery low voltage so am guessing the central locking battery is going to need replacing shortly).

Have done the N249 bypass but have left it electrically connected to prevent it throwing up any fault codes.

According to the link there is 10 tests to run, when it comes to this test
2.8.8 Block 046 - Catalytic Converter Diagnosis
Enter the Basic Settings block 046.
Field 2 indicates the CAT Temperature (EGT), which must be more than 320°C
for the test to start. Increase engine speed if necessary.
Field 3 is the CAT Conversion Efficiency. If the cat is good, the value should be
below 0.50 at the end of the test.
The field 4 will say either 'TEST OFF/ON' before/while the test is running, and
either 'CAT B1 OK' or 'CAT B1 NOT OK' afterwards.
Do not continue with testing unless the field 4 is indicating “CAT B1 OK”.

Field 4 just says "TEST OFF", field 2 was reading about ~375°C and field 3 was reading 0.13 iirc. (Will run again and take screen shots this time). To me that reads as the CAT is healthy but the test hasn't run - as a note I left it for approx 10mins in this block to allow plenty of time for the test to run.

After waiting for the 10mins or so I came back out of the basic settings and checked the readiness block and the first 9 tests all said passed, it was the last test (for the CAT) that had failed/not ready.

As for the lambda I think it was just the MOT centre guessing the lambda and CAT had failed and not done any conclusive testing as from the tests above all appears well apart from the CAT.

Hope this makes a bit more sense as not the best at explaining things.
Gaz
 

aragorn

"Stick a V8 in it!"
Staff member
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Its pretty unlikely to be BOTH the cat and the lambda.

What were the numbers on your failed emissions test? Ie CO, HC, Lambda etc
 

S3 Nattie

Quattro ist für sissies
I tried to do the test the other day and it stopped in the same place as your refering too and all my cat stuff fail in the readiness checks.

Nathan
 

thorsy22

Registered User
I'd have to look at the failure when I get home as am at work atm.
 

thorsy22

Registered User
I tried to do the test the other day and it stopped in the same place as your refering too and all my cat stuff fail in the readiness checks.

Nathan

When were you looking in the readiness block Nath?
I looked before i started the tests and quite a few were failed/not ran but I believe that was because the car wasn't up to temp. I waited till the temp needle was at 90. Need to make sure the exhaust temp is over 350C iirc before some tests will start.

If you followed the procedure if one failed in all likelihood you'd need to replace that sensor before carrying on as it would be causing the other readings to be off. I'd start at the beginning and work through them again, when your failing either take the sensor out to clean or replace and re-run to check it passes and move on. Should be a systematic approach and believe the tests run from front to back through the exhaust system to help pick out just which part of the system has a fault.

Next time I have a day off I'll re-run the tests and try to take a screenshoot of each stage for reference and to help explain things a bit more.
 

S3KO4

Registered User
Didn't Welly have high emission at some point, which lead back to the bypass of the N249? I could be wrong.
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator

thorsy22

Registered User
There's no specific values for co hc lambda as says test was aborted, and the wordingon the MOT failure is "exhaust emissions carbon monoxide content after 2nd fast idle excessive [7.3.D.2b]". Hope this helps, hopefully will re-run the tests tonight and take some screen shots of each test.
 

aragorn

"Stick a V8 in it!"
Staff member
Moderator
VCDS Map User
ffs thats a crock.

If they'd actually given you the values you'd have a much better idea of whats going on.

On a stock car, with no fault codes, and slightly raised CO (around 0.5 usually) i'd say the cats failed. If the CO is properly high (1.0+) theres something else wrong.
 

thorsy22

Registered User
It is kinda but I suppose if it's stupidly high it's not worth running as something is obviously wrong.
My mechanic did say that it was stupidly high, think something like 10* which would be 3.0+??
 

thorsy22

Registered User
Slight update on this, didnt have time to run all the cat tests earlier, but having a quick look in measuring block 46 turned up something very interesting.
cat.jpg


5c? I think not! :noway:

The question is would a low temp reading cause the ecu to over fuel to help warm the engine up and there push the emissions up?
Secondly what temp sensor what that be and where is it located?
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
Looking at that the car isn't even warm yet... I would imagine the water temp would need to be at 90deg before the test is valid...

According to the TT pdf...
Before starting, the following conditions must be met:
&#8226; No DTCs
&#8226; Battery voltage at least 11.5V
&#8226; Coolant temperature at least 80°C
&#8226; All electrical instruments switched off
&#8226; Air conditioner switched off
&#8226; Engine stopped, ignition on
&#8226; Vehicle stationary; don&#8217;t do it while driving!

Your engine is running (idling) according to your screen shot and not at 80deg...

I would be tempted to let your car get warm, take it for a 'spirited' drive then pull over and do the test... EGT's can be logged on block 112... cats need to be hot to work...

<tuffty/>
 

thorsy22

Registered User
Should say, wasn't really a test but looking in the measuring blocks at this point, (only did the throttle body reset and first couple of tests another 5/10mins after this was taken) but the car had been idling for about 10/15mins at this point.

Surely even after turning the car on, the temperature should be reading more than 5'C?

EDIT: Will try and do a full set of tests on a properly warmed up car as and when I can between work.
 
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