StevenMac

Hi everyone. I just registered to seek help with this problem. I have an 2003 A4 3.0 6-spd. with 115k.

I just spent a couple of days replacing the DS wheel bearing and CV axle--finished up that job and started the car to do a test drive. Immediately, I got a flashing engine light, engine sounded weird, and I killed it. Started it again and the it died on its own after a couple seconds. Also, with the key on but car off the fan was blowing crazy.

I checked codes and got:
-Misfire on cylinders 1, 4, and 5
-Random/Multiple cylinders misfire
-Coolant temp sensor signal too high
-Implausible engine temp msg from inst. panel
-Engine start blocked by immobilizer

I popped the hood and the only weird thing I saw was a small coolant leak from a valve right up front top. I haven't started it again because I don't want to do damage. If I return the key to the ON position, though, the fan blows full blast intermittently.

Any ideas or guidance is much appreciated. Worst timing ever, as I'm getting married in a five days and all of our family is coming to town.

StevenMac

Anybody have a clue for me?

dodat

Sounds like a water pump failure and if the car registered those codes, it could be severe. Suggest you flat bed the truck to the mechanic for analysis.

StevenMac

It's also been suggested that it could be the ECU gone bad (particularly because of the fan going haywire like that). Does that sound plausible?

lyleswk

Not familiar with the 3.0, but wouldn't jump to the ECU without some simple troubleshooting. The fan running could simply be the coolant sensor. I would start there.

StevenMac

I had to set the whole problem aside until after my wedding and out-of-town visitors. So, I'm back to it. If I turn the key to ON the fan goes wild and the dash lights go on and off intermittently. Again, this makes me suspect the ECU. If anyone has had experience with the ECU on one of these, please let me know. I don't see how a water pump failure would cause the electrical problems. And while I know the temperature sensor has a history of failing, I don't see how that would make the dash lights act weird. Thoughts?

lyleswk

If your ECU was bad, not sure you would be able to get codes. Someone help here.

Start simple. You have a good battery? And exactly what lights are flashing. Jut the immobilizer light?

StevenMac

Update: I replaced the green coolant temp sensor. Initially, the symptoms remained the same. Then I cleared codes, unhooked the battery and let it sit as long as dinner. When I hooked it back up, it seemed okay, so I started the car. It started a little rough, and flashed a few lights at first, but then settled into normal. I've since driven about 40 miles and all seems good. It really surprises me that the coolant temp sensor could instigate so many other problems, and I thought it might be helpful for others to hear about it. For replacing the sensor I used a DIY here. Very helpful. Thanks to everyone who chimed in.