A3 fans constantly running after new fan module/ full unit

[Dan5115]

2004 Audi A3 3.2 fans occasionally run constantly till battery dead or f8 fuse pulled. I’ve had an auto electrician, and an Audi mechanic look at it and both told me it was fan module so I replaced with new unit and it was fine for first week then it was doing exactly the same as before.

My garage has given up and said they do not know what it is so I’ve also replaced the fan switch? In the lower coolant hose on the off chance it may have been faulty but no change.

Can anyone help me with the diagnosis of this annoying fault I can’t seem to pinpoint? Any help would be greatly appreciated

 

[Gm95]

Don't know how much help I'll be as newer cars will have all sorts of modules and electronic gimmicks to do different things but I had the same issue on an old Celica I had, I imagine the premise is basically the same? That would send the fans on as soon as the battery was connected and the fan was controlled by a circuit with a couple of relays.

They were wired in a fail safe way so that if something caused the circuit to break (Switch open) it would provide power to the fan. It's like if something went wrong, you would rather the fan always be on than never be on and overheat.

To sort that, I found a wiring diagram online, printed it out, stuck it on the wall and studied it, checking with a multimeter at relays/switches to find out where the circuit was open. In the end, I found out that there was a plug that would go into a part of the AC system for some reason and the previous owner had got rid of the AC for the extra 5bhp.. They had just left this plug dangling in the bay, not plugged into anything. That was were my open circuit was. When I put a jumper across the two pins, the fan went off.

Again, not saying this will be the same case with A3's but I imagine there's the same sort of 'fail safe' system in place. I would check all plugs to check they're not damaged or not pushed in properly. Also see if you can find a wiring diagram online for the fan? With anything like this, a multimeter is your best mate

Hope this helps a tiny bit lol.

 

[Dan5115]

Don't know how much help I'll be as newer cars will have all sorts of modules and electronic gimmicks to do different things but I had the same issue on an old Celica I had, I imagine the premise is basically the same? That would send the fans on as soon as the battery was connected and the fan was controlled by a circuit with a couple of relays.

They were wired in a fail safe way so that if something caused the circuit to break (Switch open) it would provide power to the fan. It's like if something went wrong, you would rather the fan always be on than never be on and overheat.

To sort that, I found a wiring diagram online, printed it out, stuck it on the wall and studied it, checking with a multimeter at relays/switches to find out where the circuit was open. In the end, I found out that there was a plug that would go into a part of the AC system for some reason and the previous owner had got rid of the AC for the extra 5bhp.. They had just left this plug dangling in the bay, not plugged into anything. That was were my open circuit was. When I put a jumper across the two pins, the fan went off.

Again, not saying this will be the same case with A3's but I imagine there's the same sort of 'fail safe' system in place. I would check all plugs to check they're not damaged or not pushed in properly. Also see if you can find a wiring diagram online for the fan? With anything like this, a multimeter is your best mate

Hope this helps a tiny bit lol.

Thanks for your reply, kinda makes sense that they may be running in some kind of “fail safe mode” just weird how it’s intermittent and they operate fine sometimes then others they don’t. I do recall a fault code stating “30amp open circuit” or something a while back when I did a vcds scan maybe this is related more than I initially thought. Cheers

 

[Gm95]

Thanks for your reply, kinda makes sense that they may be running in some kind of “fail safe mode” just weird how it’s intermittent and they operate fine sometimes then others they don’t. I do recall a fault code stating “30amp open circuit” or something a while back when I did a vcds scan maybe this is related more than I initially thought. Cheers

Best of luck! Let us know when you find the answer.