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2008 A6 4.2 cooling fan staying on continuously after shut off
Had this start today. The radiator fan on the drivers side is running continusouly after I shut down the car. I checked the coolant temp with VCDS and it is reading in normal ranges (75c down to 62C before I stopped looking at ti). If I open the door, the fan will go off for a few minutes and then come back on. I found the relays under the dash on the dirvers side and pulled each one but none of them shut the fan off. I also pulled the fuse for the AC but that didn't shut it off either. I guess the other fan is the AC condenser fan. I disconnected the battery so it doesn't run until it's dead. I can't find much info on where there are other relays. I did vcome across an article that the sealed box on the drivers side by the windshield has relays in it and if water gets in there, this can happen. Anyone know for sure about that? That is all I can think of next besides changing the coolant temp sensor, but I don't think that is it.
I also saw some articles about two coolant emp sensors. One for the fans and one for the guages. I went through a lot of measuring blocks in VCDS and only saw the one for the G62 temp sensor. Woudl definitely appreciate some help on this one.
No matter what, I think you’ll have to inspect that fuse box. That was one of the first preventive actions I did after purchase. Be very cautious on re-assembly, it’s very tricky to get it back properly! It’s a pita to get it out as well (no space to work). Clean dirt around it, inspect does the water goes down the fender while you are there.
Good news, bad news. I was able to check all 3 things I wanted today (collant temp sensor and two boxes under the cowl. No water anywhere but none of the relays controlled the fan. Will keep researching for other relays and will look at the fan control module next. Always fun when you have to spend 20 minutes getting the wiper blade off to get to the fuse box/relays. Also nice that Deiter didn't put what the fuses go to anywhere in the service book. Thanks Deiter.
Other symptoms I noticed today.
When I first ocnnected the battery this morning, the fan came on immediately.
I put a battery tender on the battery overnight (it was disconnected, otherwise the fan would have run forever I would guess). I connected it to move the car this evening. It ran for less than 3 minutes. I parked it and didn't disconnect the battery. I waited and it came on after ~10 minutes.
It will go off if I open the door or start the car.
I have the AC system off.
And just for completeness, I ran a VCDS scan. Came up with some old stuff and that the coolant temp sender was implausible but no smoking un on any control modules.
Hmmmm....wracking my brain troubleshooting. Did a search on parts.audiusa.com for fan relay and it has a listing (https://parts.audiusa.com/productSea...=fan%20control). In the details, it says 2008-09 Power Module. The part number links to a 645 fuse: https://www.audipartsstore.com/oem-p...lay-4h0951253a.
And also looked in my owners manual and there is an index entry for Radiator fan. It says:
The radiator fan switches on automatically by itself (in italcs for emphasis even)
But also foes on to say the radiator fan is driven by the engine via the v-belt (not true for the 4.2).
An auxiliary fan switches on and off depending on the coolant temperature and other vehicle operating conditions (thanks for the specific Deiter)
After you switch the engine off, the aux fan can continue running for up to 10 minutes - even witht he ignition off. It can even switch on again later by itself if,
- The temperature of the engine coolant rises due to the heat build-up from the engine in the engine compartment or
- the engine compartment heats up becuase the vehicle is parked in intense sunlight
This points to either the coolant temp sensor or some control unit that I have not yet identified (unless its the power module)
Yahtzee. Went back out and poked around in the passenger side plenum box (As it is called). Found two more 643 relays wrapped in foam. Pulled the one on the right and the fan stopped. Swapped with the one on the left and the fan did not come back on. What a PITA. I don't see any moisture in there and the other relay right next to it seems fine. Luckily, my office is ~5 minutes from an Audi crack dealer so should be able to pick up a replacement tomorrow and be done with this. Sheesh.
I guess the 643 relays are superceded by the 645. $43.37 for a 645 relay. Glad it wasn't a 900 relay, I guess that would be closer to $80. Off to the garage to put it in and put it all back together. What a pain, but at least I learned where more fuses and relays are hidden.
Always takes longer to put stuff back together because I like to clean everything. I missed all the butt connectors when I first found the relays last night. I looked closer today and it definitely looks like someone was in there doing some wire work. Both relays had cut wires and butt spliced back to the main harness. One was really loose and separated so I soldered it. I left the other ones alone since they seemed ok. I also noticed some water at the bottom of the box. I couldn't get anything down there to wipe it so I used an air blower from my compressor to get rid as much as possible. Got it all back together and let it run up to temp and the fan came on and not at full speed. One of several butt connectors The water is the shiny looking piece at the middle right Cleaned plenum cover Cleaned plenum cover
Off topic and might be the lighting but is the brake fluid dark color and maybe turning green? If so then the hydraulic system needs a flush and afterwards the pedal will be less spongy.
09-24-2023, 05:19 PM
2008 A6 4.2 cooling fan staying on continuously after shut off
