Frustrating Intermittent ECU / Electrical Problem!

[andyhart21]

Hi everyone, I have owned my 2012 4L Q7 for around a month now and love it to bits. I have a really frustrating intermittent electrical problem and I'm hoping someone can point me in the right direction. I'm not an idiot when it comes to electrical problems on cars and have my own diagnostic gear, but I'm by no means an expert with the Audi Q7. I'm also an electrical/electronics engineer by trade, so I like to think I can have a decent stab at diagnosing things, but this has me a bit stumped.

I bought the car from a dealer, who put a new stop/start battery on the car before I collected it, and that is when these issues started (although that could be a complete coincidence).

75% of the time when the car has been stood overnight (it does not normally do this if the car has been stood for around 8 hours in the day when I'm at work), when I turn the ignition key to the first position, I get a white small gear symbol on the display (see photo). If I then start the car, it will not let me come out of park. If I don't start the car and turn the ignition off and back on again, it is fine. If I start it and turn it off and on again, it is fine. I did fault code scan the car when it had the gear symbol on the display, and it returned 3 fault codes as shown in the first attached log file.

Now this had also started happening to the dealer before I collected the car. His local transmission specialist diagnosed it as a faulty transmission selector module, and replaced it with a brand new one at a cost of around £500 to him (I have the invoice). This did not happen again until a few days after I got the car home, and now it happens again most days. If this was the only fault, I could probably live with it TBH as it isn't that inconvenient, albeit a bit frustrating. 

However, on 2 occasions it has turned into a bigger fault. On these occasions, when the ignition is turned to the first click, I get a large yellow gear symbol indicating a transmission fault and reduced functionality. When I fault code scanned the car with this fault standing, I got many fault codes with many different ECU's as shown in the 2nd attached log file. These fault codes mostly seem to indicate intermittent communication faults between different ECU's.

Until these faults are reset with my laptop, I get reduced functionality on many things, and the car is unusable. I am having to carry my laptop around with me in case this happens when I am out. 

This one is obviously more of a concern, and my thoughts are that it is definitely connected to the first fault. I am thinking rather than it being a genuine fault with the transmission, it could possibly be a communication issue between the ECU's, possibly a faulty main ECU, possibly a faulty transmission ECU, possibly water ingress, or possibly damaged wiring. Then there is also the possibility it is connected to the replacement of the battery? I did recode the new battery to the battery control module to reset the adaptations when I first got the car, so it's unlikely to be anything to do with that.

Can anyone think of a good place to start looking? I know these cars can suffer water ingress around the ECU's under the seat due to blocked drains, so I'm going to look there at the weekend as a starting point, but after that I'm struggling. The problem is that everything resets just fine and then remains fine until it has been stood overnight.

Any help or advice would be massively appreciated, and if any of you are local to the Chesterfield area and need your car scanning, just ask.

Thanks in advance

Andy

Log File 1.txt Log File 2.txt

[Stevey Y]

33 minutes ago, andyhart21 said:

Hi everyone, I have owned my 2012 4L Q7 for around a month now and love it to bits. I have a really frustrating intermittent electrical problem and I'm hoping someone can point me in the right direction. I'm not an idiot when it comes to electrical problems on cars and have my own diagnostic gear, but I'm by no means an expert with the Audi Q7. I'm also an electrical/electronics engineer by trade, so I like to think I can have a decent stab at diagnosing things, but this has me a bit stumped.

I bought the car from a dealer, who put a new stop/start battery on the car before I collected it, and that is when these issues started (although that could be a complete coincidence).

75% of the time when the car has been stood overnight (it does not normally do this if the car has been stood for around 8 hours in the day when I'm at work), when I turn the ignition key to the first position, I get a white small gear symbol on the display (see photo). If I then start the car, it will not let me come out of park. If I don't start the car and turn the ignition off and back on again, it is fine. If I start it and turn it off and on again, it is fine. I did fault code scan the car when it had the gear symbol on the display, and it returned 3 fault codes as shown in the first attached log file.

Now this had also started happening to the dealer before I collected the car. His local transmission specialist diagnosed it as a faulty transmission selector module, and replaced it with a brand new one at a cost of around £500 to him (I have the invoice). This did not happen again until a few days after I got the car home, and now it happens again most days. If this was the only fault, I could probably live with it TBH as it isn't that inconvenient, albeit a bit frustrating. 

However, on 2 occasions it has turned into a bigger fault. On these occasions, when the ignition is turned to the first click, I get a large yellow gear symbol indicating a transmission fault and reduced functionality. When I fault code scanned the car with this fault standing, I got many fault codes with many different ECU's as shown in the 2nd attached log file. These fault codes mostly seem to indicate intermittent communication faults between different ECU's.

Until these faults are reset with my laptop, I get reduced functionality on many things, and the car is unusable. I am having to carry my laptop around with me in case this happens when I am out. 

This one is obviously more of a concern, and my thoughts are that it is definitely connected to the first fault. I am thinking rather than it being a genuine fault with the transmission, it could possibly be a communication issue between the ECU's, possibly a faulty main ECU, possibly a faulty transmission ECU, possibly water ingress, or possibly damaged wiring. Then there is also the possibility it is connected to the replacement of the battery? I did recode the new battery to the battery control module to reset the adaptations when I first got the car, so it's unlikely to be anything to do with that.

Can anyone think of a good place to start looking? I know these cars can suffer water ingress around the ECU's under the seat due to blocked drains, so I'm going to look there at the weekend as a starting point, but after that I'm struggling. The problem is that everything resets just fine and then remains fine until it has been stood overnight.

Any help or advice would be massively appreciated, and if any of you are local to the Chesterfield area and need your car scanning, just ask.

Thanks in advance

Andy

Log File 1.txt 4.89 kB · 0 downloads Log File 2.txt 23.19 kB · 0 downloads

Hi if I were you I would go back to the beginning, you mentioned that they fitted a new battery, did they recode the new unit to the car as especially on Q7/Q5 this will throw up all these type of communication codes, I worked on a Q5 recently that had similar problems and it turned out that the battery was going sideways, not only was it a cr@p brand the mobile pillock that fitted it told the owner they dont need coding as they sort themselves out, WRONG!,I fitted a Bosch battery and that was over two months ago and coding it successfully made all the faults go away, what leads me to this is the fault codes you published which state intermittent which I would read as possible low voltage faults, if the battery was not coded it charges at the same rate as it did with the failing battery and effectively cooks it because no one has told the ECU it has another battery, the other thing to try is clean all the connector plugs on the ECU as they are prone to moisture ingress which they are not to keen on, I could be very wrong as Q7s are notorious for ECU failure.

Steve.

[andyhart21]

46 minutes ago, Stevey Y said:

Hi if I were you I would go back to the beginning, you mentioned that they fitted a new battery, did they recode the new unit to the car as especially on Q7/Q5 this will throw up all these type of communication codes, I worked on a Q5 recently that had similar problems and it turned out that the battery was going sideways, not only was it a cr@p brand the mobile pillock that fitted it told the owner they dont need coding as they sort themselves out, WRONG!,I fitted a Bosch battery and that was over two months ago and coding it successfully made all the faults go away, what leads me to this is the fault codes you published which state intermittent which I would read as possible low voltage faults, if the battery was not coded it charges at the same rate as it did with the failing battery and effectively cooks it because no one has told the ECU it has another battery, the other thing to try is clean all the connector plugs on the ECU as they are prone to moisture ingress which they are not to keen on, I could be very wrong as Q7s are notorious for ECU failure.

Steve.

Thanks Steve, I had wondered this myself. I did code the new battery to the car as the dealer hadn’t done it, but it didn’t have a BEM code on it so I had to guess the code. I was told as long as the code changes, this resets the adaptations, but I could not see the brand of battery when I looked under the seat so have no way of knowing if it is decent or not. I’ll pull the battery out and have a look but I doubt it’s a top quality one. The symptoms certainly point to being voltage related that’s for sure. I’ll order a decent new battery anyway and give it a go I think. 
 

Cheers

[Stevey Y]

1 minute ago, andyhart21 said:

Thanks Steve, I had wondered this myself. I did code the new battery to the car as the dealer hadn’t done it, but it didn’t have a BEM code on it so I had to guess the code. I was told as long as the code changes, this resets the adaptations, but I could not see the brand of battery when I looked under the seat so have no way of knowing if it is decent or not. I’ll pull the battery out and have a look but I doubt it’s a top quality one. The symptoms certainly point to being voltage related that’s for sure. I’ll order a decent new battery anyway and give it a go I think. 
 

Cheers

Hi I am not sure which diagnostic platform you use but I use VCDS for the earlier cars and OBD Eleven for the later cars both these show the original BEM code which allows you to change the last two digits which allows acceptance by the ECU, the OBD has the simple system to recode and even if your battery is not listed gives the UNK unknown option, you also have to enter the cranking amps etc so the ECU has the whole story, then its happy, the Q5 I did the battery was only six weeks old but the overcharge had killed it. The electronics on this brand are to say the least complex and rely on strict adherence to repair strategy to perform properly, if you can lift the right code it makes life easier.

Steve.

[andyhart21]

14 minutes ago, Stevey Y said:

Hi I am not sure which diagnostic platform you use but I use VCDS for the earlier cars and OBD Eleven for the later cars both these show the original BEM code which allows you to change the last two digits which allows acceptance by the ECU, the OBD has the simple system to recode and even if your battery is not listed gives the UNK unknown option, you also have to enter the cranking amps etc so the ECU has the whole story, then its happy, the Q5 I did the battery was only six weeks old but the overcharge had killed it. The electronics on this brand are to say the least complex and rely on strict adherence to repair strategy to perform properly, if you can lift the right code it makes life easier.

Steve.

I use VCDS Steve. This was the sticker on the top of the new battery, but I could not see any of the side stickers to get a brand. The invoice from the seller didn’t indicate a brand either. Out of interest, do you know what brand the OEM Audi batteries are? I’ve read Varta, but obviously I didn’t see the original battery to confirm.