Case Study: Do you have a P0442 or P0456 - Evap leak?

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DrPeter

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Hello,

So I had been putting off the diagnosing a check engine light on my wife's 2006 A3 2.0L with the BPY engine, simply because I know the fault code (see below) was for a small/very small evaporative emissions system leak, last few times I have checked.

She had been telling me for a while now that the light comes on and then goes off. I was curious as to what was going on at first because I had just recently completed a good amount of engine work and I wanted to make sure that nothing was wrong.

See this thread for more information about the work I had done this spring.

2006 Audi A3 BPY 200,000 mile service


All the work I did was okay and I finally decided to do some testing! Here is how I went about testing the Evaporative Emissions System on the 2006 Audi A3 and these simple tests can be applied to a wide range of vehicles, since there are fundamental similarities with most VAG group vehicles.


When diagnosing any Evaporative System leak, I first recommend to verify gas cap is tight. Obvious, but some times we as humans over look the obvious.

Next, start the engine, loosen and tighten the fuel tank cap.

With VCDS, select Engine, then Basic Settings and then enter the BS group number [071] for the BPY and other gasoline/petrol engines.

You can use the pull down menu with VCDS if you do not know the group numbers or if the Engine controller is UDS there will be no group numbers, in that case you have only pull down lists. Some engines use the Basic Setting group number [202], block (4) will display [xxxxx100] when the test has passed.

The Basic Settings Test will activate the Leak Detection Pump (LDP) for a period of time, stopping when the reed contact in the LDP pump opens, when fuel tank pressure has reached about 25mbar for most systems. The LDP is vacuum driven, so the Engine needs to be running and have no vacuum leaks.

The ECM will now wait until the reed contact points close, if the time is less than about 1.2 seconds, the ECM detects a 'Large Leak' and will test the system three more times in most cases to verify the results. If the system takes a little bit longer to leak down and open the reed contacts, (about 1.2 to 3.2 seconds), the ECM has detected a 'Small Leak'. Times may vary with different ECMs, however the principal is the same, the ECM commands the LDP to operate, then waits a certain amount of time and based on the results will pass or fail the test.


If the test fails, I pinch off and hold the (soft) hose between the N80-Canister Purge Valve and the charcoal canister and run the test again.
- If at this point the test passes, you can suspect a concern with the N80 valve. Remove the N80 and check for tiny bits of carbon from the evaporative systems charcoal canister.

In my case the test still failed when I pinched off the hose to the N80 valve.





The next thing I did was to have a closer look at the fuel tank cap. What I saw was rather interesting, click on the image for a closer look!




As you can see, there is a rubber sealing ring and as it is at least 13 years old, it has failed/cracked.

So I decided to try one more thing, I ran the Basic Setting test again, this time I was pressing the fuel cap into the filler neck with some pressure. When the test finished, it passed! "System Okay"..

Need a new fuel cap, right.. Sure you can spend $44.40(MSRP) for a brand new fuel cap, part number [8P0-201-550-D], but I looked a bit further and found that there is actually a replacement sealing ring, it is an updated part and for a low as $10.77 and ten minutes of work, I was able to fix the concern.

The part number [191-201-557], fits almost every Volkswagen, Audi threaded fuel cap from 1947 to 2010!.. I was shocked to see that..




Code:
Address 01: Engine        Labels:. 06F-907-115-AXX.clb
   Part No SW: 8P0 907 115 B    HW: 8P0 907 115 B
   Component: 2.0l R4/4V TFSI     0080  
   Revision: --H10---    Serial number: AUX7Z0E8FN6015
   Coding: 0103010A1C070160
   Shop #: WSC 66565 257 00032
   VCID: B1251682282F8BC7A6-80E4

2 Faults Found:
001110 - EVAP System 
               P0456 - 001 - Very Small Leak Detected - MIL ON
             Freeze Frame:
                    Fault Status: 11100001
                    Fault Priority: 0
                    Fault Frequency: 2
                    Reset counter: 255
                    Mileage: 318088 km
                    Time Indication: 0
                    Date: 2019.06.12
                    Time: 09:22:43

             Freeze Frame:
                    RPM: 770 /min
                    Load: 13.3 %
                    Speed: 0.0 km/h
                    Temperature: 75.0°C
                    Temperature: 27.0°C
                    Absolute Pres.: 980.0 mbar
                    Voltage: 14.224 V

001090 - EVAP Emission Control Sys 
               P0442 - 001 - Small Leak - MIL ON
             Freeze Frame:
                    Fault Status: 11100001
                    Fault Priority: 0
                    Fault Frequency: 1
                    Reset counter: 255
                    Mileage: 318633 km
                    Time Indication: 0
                    Date: 2019.06.18
                    Time: 09:47:55

             Freeze Frame:
                    RPM: 834 /min
                    Load: 19.2 %
                    Speed: 0.0 km/h
                    Temperature: 67.0°C
                    Temperature: 30.0°C
                    Absolute Pres.: 980.0 mbar
                    Voltage: 14.224 V

Readiness: 0000 0000

This is tech tip, a giude, there are a lot of things that can fail on the evap system and this post is meant to help you eliminate a few things. If you need help, post your questions here, Car Repair Support, in the Ross-Tech forum.


Hope this helps,

drpeter
 
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