axl3133

Hi, was hoping I might be able to get some insight here.. I have an 07 Q7 4.2 with 105K. Last week during frigid cold here in Boston the car stalled shortly after starting up. Did this a few times then seemed ok. Later while driving it completely cutout and would not start or even turn over. Had it towed home. Car will not crank now and I am getting a low battery warning on the dash, esc fault, and adaptive headlight fault. When I put the key to the on position the fan comes on at a very high speed. Also, very weird, the CD changer starts going through the discs. It is a stock radio. All other electrical in interior is fine, lights etc.. The battery tested bad, so I replaced it, was almost time for a new one anyways. There is no communication from the OBD port. I checked for power and ground there and got 12V. But when I checked pin 7 got nothing. So far I have checked all fuses and tested all relays save the few next to the steering column. Anybody have any tips for the next diagnostic steps? Thanks!

Edd W

Try disconnecting the battery ground lead for a few minutes then when you re-connect it, make sure it connects well straight away with no flickering on and off. It sounds like there is some logic corruption somewhere to me....

axl3133

Thanks Edd, when I take off the ground from battery and reconnect, I do get a bit of flickering. Also should mention I did a parasitic drain test and after 5 minutes there were no drains.

axl3133

Just realized the passenger side floor is soaked after rain. I am going to clean the drains today. Water seems to be coming in just under the glove box. What is over there in terms of electrical that could cause this?

smith2010Q7

check under the passenger seat. You have two control modules that can cause your problem.
1. Vehicle Electrical System Control Module 2 -J520-
2. Transmission Control Module (TCM) -J217-

axl3133

Ok will do. I actually have the seat partially removed as I was heading there anyways. Once I find these modules, how does one test them?

Dtomasi

Sounds like the alternator quit. See if you can get a good battery or fully charge the one you have and see if the car starts. If it does start let it run for a minute and then pull the positive cable off the battery while it's running and see if it cuts out, if it does then you know if its your alternator.

axl3133

Thanks for the reply. I dont think its the alt only because all electrical is fine in the car.

smith2010Q7

need to scan for codes to see any areas if TCM is bad or the Vehicle Electrical System Control Module 2 -J520- .
example:
Perform Guided Fault Finding or Guided Functions before replacing or removing the control module. Refer to vehicle diagnosis, testing and information system VAS 5051.
Read out the control module identification and coding from the previous transmission control module (TCM) (J217) and J520.

axl3133

Thank s so much again for taking your time to help me out. I probably should have mentioned I am not a pro, just a guy trying to rule out as many problems before this car gets shipped to the dealer. As I mentioned previously, there is no communication from the car. I have checked for power and ground at the port and its fine. I am wondering how to physically check the j520. Looking at the pin assignment on the j520 I see only a few pins used. However, one caught my attention which is the glove box unlock motor activation. Mine is currently not working and was before. I guess my question is.. if I check for power and or continuity at pins 105 and 113 (can-h and can-l) will that give me aome insight as to the functionality of this module (j520)? Sorry in advance if this is a completely ridiculous and naive question. Thanks again