carlzimmerman

As expected, after a week of testing by the top mechanic at Audi of Charlotte, they have determined that it is the ECU that needs to be replaced. The ECU would pass all the tests when it is cold, but when it heats up it gives the error code. I am having i replaced with an OEM ECU from Audi - $1,700. My rationale is A.) I already have $260 tied up in diag time that goes toward it B.) it's still cheaper than getting a new car.

If you do not hear from me, it's because I will have turned a new leaf with a CEL free dashboard.

ILLusive

Wow, so a used ECM won't fix the problem, but a brand new ECM will? $1700 is a lot of dinero. Did they even try upgrading the firmware first or did you already have the latest ECM firmware?

A6Gary

Do you know how the Audi tech determined the problem was in fact the ECU, such as bad/no output signal, failed wiring, measured block reading, etc.? If have them replace the ECU, does the Audi dealership GUARANTEE that this repair will fix the problem forever? And if the DTC returns, will they refund the ECU repair cost? If the ECU is REALLY the problem, then I believe that all of us C6 A6 owners that have had this problem should hit A of A with a claim because that part is critical to an emissions compliant system, which VW/Audi is already under intense scrutiny and criticism for Dieselgate. Note that the emission system is warranted for 8 years/80,000 miles, so it does provide a basis for A of A to deal with this repair as a manufacturing defect.

carlzimmerman

I have now driven three days in 94 degree weather and it has not come back on since they put in the new ECU. The service guy said he never wanted to see me again unless it was for service because they spent so much time diagnosing it. P2404 code no more - I actually remember the first time it came on in 2013. I am also getting much better gas mileage and it's running a lot smoother - or maybe it's just my imagination.

A6Gary

Thanks for the update. Hope that the new ECU resolves this problem for you. How many miles have you driven since it was replaced? The largest mileage interval for this DTC appearing on my '06 A6 Avant was a little over 700 miles. Now the DTC is appearing in less that 200 miles of driving. If possible, please provide updates as you add miles and if the P2404 PIA ever appears again.

ILLusive

Yes! PLEASE give us periodic updates til maybe the end of the year and if it doesn't rear its ugly head by then, we all know its faulty ECM and maybe we can have a strong case to bring to AoA.

carlzimmerman

Here is what the report from Audi said:

ECM ISSUE SAME FAULT AS BEFORE. REMOVED LEFT REAR WHEEL AND FITTED TO LENGTH. FOUND VACUUM HOSE TO LDP PUMP HAD FOLDED OVER. REPAIRED AND FITTED TO LENGTH. RERAN TEST- DID NOT PASS. CHECKED WIRING AND FOUND RED AND BROWN T17 PIN CONNECTORS HAD CORRODED PINS. CLEANED, PUT STABILANT ON TERMINALS AND REFITTED. RAN TESTS- DID NOT PASS EXCEPT FOR ONE TIME WHEN COLD. WHEN VEHICLE HEATED THE TEST WOULD FAIL. REMOVED ECM AND PLACED INTO REFRIGERATOR AND LET SIT FOR 1/2 HOUR. TRIED AGAIN AND THE 71 TEST PASSED. ORDERED AND INSTALLED NEW ECM- CODED AND IMMOBILIZED. RAN TESTS SEVERAL TIMES -EACH TIME PASSED. RESET READINESS CODE- GOOD. ROAD TESTED-OPERATING TO MANUFACTURER'S STANDARDS.

I have also been getting up to 30.8 mpg on the highway and 24 mph in town which I have not seen in a long time.

A6Gary

Thanks for the Audi report. The tech didn't ID the T17 pin connectors that were corroded in the report, but most likely the electrical wires to the LDP. I have run the 071 test numerous times and most of the time it passes ("System OK"). But sometimes, the test result was "ABORT". For my info, what year is you A6, how many miles on it, and what locale has it been in, e.g., marine, winter salt exposure, etc.? I am curious because this DTC initially appeared on my '06 A6 last year with ~73K miles on the car. The car has been garaged since I bought it 8 years ago, so I doubt I have any corrosion issues. I'm also looking into a weak battery (it still has the original battery!) issue that surfaced with the last CEL (DTC P1602 as well as infamous P2404). Will advise if I find anything.

occhis

FYI, I suspected a weak battery also - mine was original too. I replaced the battery about 2 months ago and still have the P2404 code.

ILLusive

Sadly, I have to bite the bullet too and have a brand new ECU installed. I have to smog the car and some of you may know, but Cali now does smog checks over OBD on newer cars, so it you have any DTCs or Readiness isn't completed, you're SOL.
Not happy about this...