quattro1432

Posted this over at the 'zine but seems there's more traffic in this Q forum. Bought an '07 Q7 a couple months ago. Everything going great, I load the family in on Saturday morning, turn the key, and get clicks. I assume one of the boys left a back seat light on overnight, so I just jumped it with my wife's car. She has to rev it a bit and then it starts up. Fast forward, we're going to leave our destination and come back home - same story. This time, we pull my sister's CR-V around, but it won't work, still getting clicks. So we bring my mom's X5 over, she revs it up, and the Q fires up again. I get home, turn off the car, and decide to test if it will start right back up again (i.e. is the battery being charged). Turn the key, and... clicks. Thinking there could be battery and/or terminal corrosion issues, so I buy a new battery the next day. Finally get under the driver's seat, only to find the battery is only 1 year old, and visually, everything looks great down there. Since then, I've charged up the old and new batteries, connected each to test separately, and right off the bat I'm getting clicks from both. The old battery held just over 11 volts when I tested it this morning after sitting all night, disconnected. I'm starting to wonder if the previous owner put a battery in but didn't re-program the vehicle to the new battery so now it's shot. But then again, it should fire right up with a new battery connected. Doesn't necessarily seem like an alternator issue because I wasn't experiencing any drains/low voltage symptoms over the past few weeks - drove fine to work all week and then Saturday morning it wouldn't start. It's gotten a little cooler here in Colorado since October, but nothing drastically cold. Again, my first thought is simply bad battery, but why won't it start with the new one connected? Thoughts?

Panzer A4

Battery definitely needs to get coded into the vehicle. VAGCom software or dealer can do this.
For some reason the car isn't smart enough to realize there's a new battery and will continually overcharge your battery eventually killing it.

quattro1432

Started up yesterday morning with new battery, drove about an hour away, stopped for a coffee, wouldn't start again. Tried to jump, no dice. Came back a couple hours later, jumped it and started right up. Got back home, turned it off, then tried to turn it on again - no dice. Came back out 3 hours later, turned the key, and it fired right up.

So I am dealing with it failing to start when the engine is warm/I've been driving a bit. I can turn the key to accessory and everything lights up and looks like there's plenty of power, but then turn to start and it just dies off instantly. Seen a couple other instances of this problem so will have to perform a deeper search and try to diagnose.

Up-it

quattro1432

Will try to take a look at these this weekend. Thanks man!

snapdragon

You say it only happens when warm but in the first post it was first thing wasn't it?
There is a problem on the A8 of similar vintage where the connection equivalent to the Q7 one shown as 16 or 23 on this diagram:
https://audi.7zap.com/en/rdw/audi+q7.../9/971-972005/
is insufficiently/inadequately crimped and gets hot when the alternator is fast charging because battery is low or when consumer current is high - and then when trying to restart the car after a quick stop but the connection is still hot, there is too much resistance in this connection and it won't crank or cranks slow. After cooling the car starts. If you find it, you can just feel it to see if it is hot when the problem manifests.

quattro1432

Correct, the original problem was a bad battery, which I believe was not coded to the car when installed 12-months ago. I installed a new battery, but the original problem seems to have cascaded into this new one. So yeah, it won't start when it's hot, but fires right up from cold... I'm thinking it could a bad starting relay or something. I'm not a huge garage-geek so I have to do a bit of research into the starting system and maybe just go by process of elimination. I'll take a look at the connections shown in the link you sent me as part of the process. Thanks a ton for copying that over.