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2008 Audi A4 - CEL

CEL P2404, P2402. Independent mechanic checked all vacuum and evap tank and gas cap: all OK. Says engine computer is problem. CO State inspection man says he can’t check further. Question is can the computer be flashed or software upgraded without going to an Audi dealer that wants $3K?

I am going to say the ECU is fine and that the independent mechanic is is wrong based on the codes you had and the fact that it appears as though the car is still running. You didn’t say, but I assume it is because you likely drove to the inspection station.

And a re-flash or software upgrade will not fix a bad ECU.

I’d take it to get another opinion. Maybe the Audi dealer. Yeah, $$$, but less than a new ECU.

Hey Mustangman,

I kind of thought that might be the problem. I sat in the mechanic’s place of business for some 3 hours waiting for a diagnosis of the CEL, for which I paid some $130.

The manager, owner’s son of the place, said the mechanic took off the wheel and did a variety of tests and concluded the ECU was bad and could be upgraded for the $3K! The more I thought about their report over the following few weeks the more I got the feeling they found a sucker with an Audi from whom they could easily make a few grand! I’m 80, a veteran, and live totally on SS and a small VA disability.

This was done 18 months ago. Colorado DMV gave me two years to get it fixed and gave me a reprieve for that time. The State testing facility did say the car passed emissions at the tailpipe.

I’ve neutralized the CEL about a dozen times since then and have driven it from Fort Collins to Monterey, CA and back late last summer and a week later to Syracuse, NY and back getting some 30 mpg at 75 mph on the interstates. Runs great while using regular octane fuel. Tested over many miles with high octane when I first bought the car two years ago but found absolutely no difference in performance nor mileage. I am the second owner as the first owner lived in Orange County, California. She had it well taken care of and records show it was reprogrammed once at around 90,000 miles. Other stuff too that would not account for the CEL.

It was damaged in a mild front end accident (?) and I believe sold through auction to the guy in Phoenix, AZ from whom I bought it. He registered it in AZ for a couple months, did repairs (left windshield fluid tank in front of LF wheel with a hole so it leaks) and advertised it on Craig’s List. I bought it right after he advertised it. Excellent station wagon; 3.2 L, Quattro.

It’s getting close to renewal registration so I believe I’ll take your advice and have someone else check it. There’s an Audi mechanic at an excellent auto repair shop that I’ve had do some tire/wheel work who has taken it out on the I-25 for checking at speed. Maybe he can find something.


Here is another option that may not work or even make sense for you. Instead of putting more money in this vehicle why not trade it in and find as low a cost lease as you can . If your repair does cost 3000.00 that amount would make lease payments for several months . Of Course you will not lease a luxury vehicle cheaply but there are many fine vehicles for low payments.

Don, I will give the benefit of the doubt to the shop that diagnosed a bad ecu… Theybwere not trying to scam you so much as they were not very good. The symptoms displayed combined with the accident tells me it may be a wiring problem not an ecu problem.

Good Luck

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Thank you for this. It’s the first reasonable possibility and without even physically looking at the car!

I shall direct attention to the wiring immediately.

Thanks again.

Loved Car Talk for many years, especially when they busted up when told by a caller who owns a Sabra or what-not!


From my source I see most P2404 fault result in replacing the leak detection pump module. This will need to be properly diagnosed, independent repair shops that focus on basic repairs may not be the place to go for evaporative emission system problems.

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Dec 21: 7 PM. Ok, thanks all. Have not found the problem with CEL yet but another problem occurred 10 days ago and I did not find a specific topic to my Audi. Haven driven over some salted roads more than 2 weeks ago I ran the car through a “touchless” car wash that really blasted horizontally, especially through the front end. I had shut the engine off prior to the wash. I then stopped by O’Reilly auto parts for a new hood support, the old having leaked its pressure. Then an bit later, like an hour or so, I heard for the very first time the cooling fans come while the car was in my garage. Never in the two years I’ve had it have then come on. Not in Phoenix at 119˚ and Nevada nor here in Colorado. Sitting in the garage the fans switched off and on three times and then I failed to listen further as I’d left to a part of the house where I couldn’t hear them. That was two Thursdays ago. This past Thursday not one electrical thing worked. I’d not driven it since I’d garaged it 10 days ago.
Battery was reading 6 volts and with a charger attached overnight it was still 6 volts. I bought a new battery today but the fans continue cycling. After the second on in the garage I’ve disconnected the negative terminal. Anyone have a suggested cause? I checked my meter for the computer codes and only the P2404 shows up.

Dec 22: update. Removed neg cable last night at 8 pm; fans running. This morning, 29 degrees 7 am; reset neg cable. Within minutes fans began!!! Removed cable.