4Driver4

FYIY, I was not arguing that heat wasn't an issue. I'm doubtful that repeated running of the test is the root cause of the failure. These things are crap, and they can fail unassisted.

A6Gary

This PIA DTC first appeared ~2 years ago this month at 73,774 miles. After checking my Bentley Repair Manual, I did the standard items that were identified, e.g., checked and replaced the N80 solenoid valve (with a Bosch unit), check the LDP resistance (in spec), started performing the 071 test, checked the relay, etc. After I checked the resistance of the N80 valve and found that it was out of the Bentley Manual spec, I purchased an OEM part and checked its resistance (it was also out of the Bentley spec of 22 - 30 ohms). With the low mileage on my '06 A6 Avant, none of the vacuum lines have deteriorated yet, so there is no vacuum leaks or other DTCs that have appeared. Since June 2015, I have been tracking the intervals for this DTC to trip the CEL. It ranges from a low of ~10 miles to the high point this last winter of 1,330 miles over a 1-1/2 month period. Since I know the EVAP system passes the 071 test and the DTC is a "implausible signal" error (meaning electrical fault), the Bentley Manual states that if everything checks out, replace the ECM (nice end point!).

In my case, when I run the 071 leak detection test after startup with the engine cold (the test must be run when the air intake is less than 90 C/194 F and the coolant temp less than 95 C/203 F), the fault doesn't appear again until I turn the engine off and let become cold again, such as overnight. I believe when you run the 071 test first, it tricks the ECM to believe the EVAP system test has been successfully run, so doesn't trip the DTC error.

It appears that Audi has fixed this problem in the newer engine models because instead running a pressure drop test with a LDP, the EVAP system is now under vacuum when the engine is started and then uses a pressure sensor to measure a pressure rise over a specified time period. So, they have eliminated the LDP and the associated support hardware/wiring found on the C6 platform. That is how the EVAP system is designed in the 2.0L TSI in our 2014 Q5. Since they changed from a pressure drop to a pressure rise system, Audi must have finally fixed the design error by eliminated all of the "extra" electrical draws on the ECM circuitry. Great news for us owners of the C6 A6!

A6Gary

I also agree that running the leak detection test repeatedly causes the fault. There must be a faulty circuit or connection in the ECM that fails over time and causes this EVAP error to occur. I don't have any data, but I haven't seen postings from any later C6 models (after MY 2006 or MY 2007) that have this problem. In checking ETKA, there are four different ECMs with new P/Ns that are noted for the for 2005 - 2007 V6 engine, depending on the VIN. Given these different ECMs, Audi may have fixed the design fault for the ECM replacements w/o a recall for the previous faulty parts!

A6Gary

Here is some input re: the power and current for the LDP. The Bentley Repair Manual specifies the following resistance value ranges for the LDP:

Contacts 1 to 3 (control circuit): 640 to 720 ohms
Contacts 2 to 3 (power circuit): 15 to 17 ohms

If you assume battery voltage of 12V is being applied to these circuits, then the maximum current for the maximum resistance in each circuit (using V = IR, where I = current, R = resistance) is:

Contacts 1 to 3: 0.017 DC amps
Contacts 2 to 3: 0.706 DC amps

The power for each of these circuits (using P = IV relationship) will be:

Contacts 1 to 3: 0.2 Watts
Contacts 2 to 3: 8.5 Watts

Per the wiring diagram, both of the circuits start at the ECM and go thru the LDP to ground (Contact 3). Unless the LDP resistance greatly exceeds the maximum value, which indicates a faulty LDP, the low heat generated by these two currents should not affect the function of the ECM, especially since there are probably larger currents in other ECM circuits that it controls. So, running the 071 EVAP test should not affect the ECM that could cause a failure by itself, unless the ECM itself had a defective circuit design and/or fabrication defect. Given the ECM P/N revisions, this supports the conclusion of a defective ECM.

dhoerl

Note that when you measure the resistance of the power circuit, you are measuring the copper coil windings. That component is inductive - not resistive. So you really need to measure the current when the component has power applied. Also, you need to know the resistance of the "driver" (assuming it's a semiconductor of some sort and not a relay). If that component has about 1V across it, with close to 1A of current, that's a Watts worth of power.

frankinstyn

So this may be a stupid question but I'll ask anyway.

Is it possible to install the new computer without taking it to the dealer?

From what I understand, it is coded to the security system so it isn't possible but on the off chance that it is...

I did purchase a used computer for extremely cheap and swapped them myself but then the car wouldn't start up. Started fine when I put the original back in.

I have now replaced every single component of the evap system except the computer itself. When I forced the leak detection pump to cycle, I managed to get through emission testing but I have since sold the car to a friend and would like a permanent fix.

dhoerl

Look at my post #116 - it MAY be possible using VCDS but its complex and I was not sure I could do it. I paid a company in NY to move settings from old to new - it cost many hundreds of dollars. That said, my problem is gone and my car is working as it should.

frankinstyn

Thank you. I saw a few pages ago that you were planning on doing that but missed the post saying that it was successful. I'll definitely consider it.

occhis

i understand that a replacement ECM would cost about$1700 at the dealer. How did your cost compare to that?

A6Gary

UPDATE: I am providing an update on this EVAP DTC thread with the information that I received from an ECM repair shop. A week ago, I removed the ECM (P/N 4F1-910-559-F, made by Siemens/VDO) from my 2006 A6 Avant, and sent to Module Experts in Jacksonville, FL for a possible repair. After they performed their diagnostics on the ECM, their representative contacted me to inform me that a chip on the board had burned out, which was the reason for DTC P2404/009220 EVAP being triggered. And because the chip was obviously securely soldered into the circuit board, it was not possible to remove it without damaging the board. Therefore, the shop could only replace the ECM with a re-manufactured unit. So, if there are no other issues with the EVAP system (N80 valve, LDP, and/or any leaks), the only fix for this problem is to replace the ECM, which obviously involves all of the coding to ensure the replacement unit will interface correctly with the immobilizer and all of the other engine systems. For my A6 Avant, I will have to re-install the defective ECM and try to find a local shop in the WA Puget Sound area that can perform the correct OEM coding (besides the dealer).

I also checked ETKA to verify part numbers, and found that Audi AG has issued an updated part number for the 2005 - 2007 A6s with either the V6 or V8 engines. For example, the newer part for my 2006 A6 is now 4F1-910-559-FX. The update indicates to me that the original ECM probably has a manufacturing defect that mostly shows up near or after the 8 year/80K mile USA emission warranty, which then transfers the expensive repair on us owners.