After run fan seems possessed

[kday]

The weather here has cooled off over the last few days after a bizarre late fall warm spell, and strangely this seems to correlate with the fans staying on after I shut the RS6 off, or maybe it's just a coincidence. Do I have an after-run gremlin?

For example, I moved the car about 20 feet yesterday, after it had been sitting overnight outside. The engine only ran for 30 seconds, yet after shutdown the fan(s) came on and stayed on longer than I had patience to stand there. The fans do eventually shut off. They also came on after a 30 minute drive.

My Ur-S4 has an after-run system, which is triggered by engine coolant temperature. It rarely turns on, and when it does it doesn't start until the engine has heat-soaked for a few minutes after shutdown. The RS6 either has a totally different system, or something is broken on mine.

Any ideas?

[ben916]

I am willing to bet it is the notorious Thermostat... Wade, care to chime in????

[4everRS]

I had a fan problem almost 2 years ago. Mine was that the fans came on full bore whenever I turned on the key, and ran after several minutes after I turned the car off. Did a t-belt job (replaceing the thermostat) and it was gone. I have no idea how a failing t-stat could cause this issue, but it sure seemed to do it for me.

[speedtrapped]

Temp sensor was my issue. It was shot, my fans ran cold or hot. Green cap sensor, and of course it's PIA to get at and replace, driver side rear just right of the MAF plug, or behind the SAI actuator. Cheap part, replace it and u wil be fine.

[Born2be]

I am willing to bet it is the notorious Thermostat... Wade, care to chime in????

Yep, same problem with mine. Replaced temp sensor 2x and it worked for a week or two. Finally third time replaced thermostat and no worries since. Had them do timing belt while they were in there even though I had 25k to go until scheduled service.

[kday]

Hmm. I'm having trouble puzzling out how the after-run system works from the wiring diagrams in the Bentley. I think some information is missing.

When you guys say the thermostat was the problem, are you talking about the mechanical thermostat that controls flow to the radiator? I don't understand how that could cause the fans to run after shutdown on a totally cold engine.

A bad sensor makes more sense (or less sense to the car, I guess). I was hoping to find it in the wiring diagrams so I could check it out with a meter. There is a sensor for the pump, but it doesn't seem to connect to the radiator fan controls.

Speedtrapped, do you have a part number for the sensor you replaced?

[speedtrapped]

I doubt it's the T Stat, that's a purely mechanical device, unless it goes bad and causes engine to over heat. The sensor is just another device that gives a voltage signal to ECU, if it goes bad incorrect voltage will make the ECU react in this case out parameter would automatically cause the cool down process with the fans. I will be back with part #.

[speedtrapped]

059919501A, there ya go.

[kday]

Awesome, thanks.

That's the only temp sensor I could find in ETKA and the wiring diagrams. It is used by the ECU and the gauge in the instrument cluster. I guess that means the ECU itself handles the after-run fan. Interesting.

One of the funny things about the Ur-S4 is the number of different coolant temperature sensors on the engine. Everybody's got their own -- ECU, gauge, after-run, HVAC, radiator fans, etc. It makes sense to consolidate, it just becomes harder to figure out from the wiring...

[kday]

There is definitely something I don't understand about the after-run system.

I just went out and did some VAG-COM measuring. This is both with the engine off (left side of voltage dip) and engine on:

http://blog.ultrameta.org/wordpress/wp-content/uploads/2011/12/afterrun.png


The ECU is seeing the coolant temperature correctly. The gauge on the cluster also reads correctly. But yet the fan starts running as soon as I turn the key to run, and continues running after I turn the car off.

Also, while I was doing this experiment, for the first time the coolant temperature warning appeared on the autocheck for about 10 seconds right after I started the car. Then it went away. (It's possible it was a coolant level warning, but I don't see why that would clear up by itself either.)

Anyone have an explanation for this?

(This after-running fan doesn't seem to be doing my battery any favors -- it was 11.2 volts before I started the car...)

[kday]

Well, it sure looks like it is only the Motronic that controls the fans after shutdown. Apparently the J271 relay is used to separately power a few things under control of the Motronic. This includes the after-run pump and the fan control modules. (It also includes the ignition coils, which is a little strange -- maybe it saved a few feet of wire.) Note that the pump is not directly controlled by the ECU -- it will be on whenever the J271 relay is engaged (run or after-run) and the ignition switch is off (so just after-run).

Here is a collage from the wiring diagrams:

http://blog.ultrameta.org/wordpress/wp-content/uploads/2011/12/rs6-afterrun.png

[Hy Octane]

A search of this topic will reveal many who have had this same problem. Have a look thru these threads and see which applies to you.
Most times its been the thermostat but also the sender has failed for some too..
http://www.rs6.com/search.php?searchid=1095561

[4everRS]

I doubt it's the T Stat, that's a purely mechanical device, unless it goes bad and causes engine to over heat. The sensor is just another device that gives a voltage signal to ECU, if it goes bad incorrect voltage will make the ECU react in this case out parameter would automatically cause the cool down process with the fans. I will be back with part #.It doesn't make sense to me either that the tstat could cause this. Its just that after this happened to me, and I replaced the tstat(w/tbelt job) my problems went away. Newer tstats are considered "fail safe" as when they do fail, they fail open.

Could there be another sensor in the coolant system that detects coolant flow? And if so, if the coolant is flowing while the temp sensor is reading a cold temp, the system gets confused (as coolant shouldnt be flowing) and goes into emergency mode? This is my theory.

[kday]

I didn't think to check for codes on this -- I'm still used to the simpler 90s vintage Audis I guess.

VAG-COM:
18613 - Performance Malfunction in Cooling System
P2181 - 008 - Implausible Signal - Intermittent

Bentley:
SAE VAG Description
P2181 18613 Cooling System Performance

G62 - Engine Coolant Temperature (ECT) Sensor

I guess my G62 is intermittent, and when the ECU saw an implausible value it went into a fail-safe mode and ran the fans all the time, even after shutdown. I cleared the codes and the fans went back to normal for now.

[kday]

Update: I replaced the G62 sensor 3 weeks ago, and have put about 1500 miles on the car since then, with no weird behavior. No fault codes, no unexpected after-run fan, and no coolant temperature warning. It seems clear that the G62 was causing the after-run problem in my case.

Ironically I do have to replace the mechanical thermostat as well, but that's because it appears to be sticking open sometimes. The gauge often reads less than 10:30 at highway speeds, going back to 12:00 in slower traffic, and the oil temperature gauge follows.

[4everRS]

Good news. The g62 anyway. Thanks for reporting your results. Sometimes threads are left hanging out there.

[mik15]

I had a fan problem almost 2 years ago. Mine was that the fans came on full bore whenever I turned on the key, and ran after several minutes after I turned the car off. Did a t-belt job (replaceing the thermostat) and it was gone. I have no idea how a failing t-stat could cause this issue, but it sure seemed to do it for me.

i had exactly the same problem, when i bought the car the fans would still run for a few minutes after i would turn it off, then i had the T-belt job done, including the T-stat and one of the cooling fans(driver side) and the fans wouldn't start after turning it off, i was quite afraid that they did something wrong....so it must be related to the T-stat...???

[kday]

Update to the update: the after-run fan came on today at shutdown after 25 minutes of highway driving in sub-freezing temperatures. That doesn't seem right to me. Didn't have a chance to scan for codes, but no CEL. I wonder if there's still something wrong.

[mik15]

something is definitely wrong, on the highway and driving on these temperatures the engine should get as cool as possible even with the fans not working at all...let us know if it throws any codes...i still think it has something to do with the T-stat, at least in my case...

[kday]

Well, I think this mystery is solved. A bad G62 *or* a stuck open thermostat can cause the afterrun fan to run unnecessarily. In fact the fan runs on high speed all the time. Apparently this is a fail safe mode. As soon as I cleared these codes, the fans spun down:

19537 - Engine Temperature too Low
P3081 - 008 - - Intermittent
18613 - Performance Malfunction in Cooling System
P2181 - 008 -

Implausibly, it seems like my previous problem was the G62 and my current problem (one month later) is the thermostat. It's possible my G62 was fine, but I did see a false overheat warning at one point, so I'm inclined to think it might have been acting up as well.

[4everRS]

Could there be another sensor in the coolant system that detects coolant flow? And if so, if the coolant is flowing while the temp sensor is reading a cold temp, the system gets confused (as coolant shouldnt be flowing) and goes into emergency mode? This is my theory.

Can anyone verify if there is a sensor of some sort that detects coolant flow? I really think there's something to this.

[Turbowned]

Rather than start a new thread, I thought I'd just post under this one. In recent weeks I've noticed my cooling fans would stay on after shutting the car off, which I found odd. I also noticed on occasion (or perhaps it was always happening and I just didn't pay attention) that the cooling fans would come on when the engine was cold. This morning, I started the car in 15 degree F weather, and proceeded to clear some ice and snow off the car. I noticed the fans were on full blast, which seemed odd considering how cold it was out. Got in the car and noticed the CEL was on.

Drove the car to work, and it got up to normal operating temp and drove just fine. Scanned it and pulled the P3081 code. The moment I cleared the code, the fans stopped running. I'm going to check coolant level first, then try replacing the coolant temp sensor. The t-stat and water pump were not replaced during the last t-belt replacement at 68k; this was prior to my ownership. Really hoping I don't have to replace the T-stat 'cause that would suck!

[Other_Erik]

Rather than start a new thread, I thought I'd just post under this one. In recent weeks I've noticed my cooling fans would stay on after shutting the car off, which I found odd. I also noticed on occasion (or perhaps it was always happening and I just didn't pay attention) that the cooling fans would come on when the engine was cold. This morning, I started the car in 15 degree F weather, and proceeded to clear some ice and snow off the car. I noticed the fans were on full blast, which seemed odd considering how cold it was out. Got in the car and noticed the CEL was on.

Drove the car to work, and it got up to normal operating temp and drove just fine. Scanned it and pulled the P3081 code. The moment I cleared the code, the fans stopped running. I'm going to check coolant level first, then try replacing the coolant temp sensor. The t-stat and water pump were not replaced during the last t-belt replacement at 68k; this was prior to my ownership. Really hoping I don't have to replace the T-stat 'cause that would suck!

Just had this odd behavior start, almost positive it's my coolant temp sensor. Had the autocheck coolant come up as soon as I turned the car on, haven't had a chance to scan yet. Fans running full blast from the time I key-on to 5-10 mins after shutting down, keeping my voltage at/below 12 when I'm idling, hoping this doesn't f-up the battery (for the 3rd time now with this car). Anyone got a simple DIY for replacing G62 that hopefully doesn't involve pulling the engine again?

Thx
O_E

[P1054]

I replaced the G62 sensor (I believe that's the little green guy on the driver side rear of the engine?) without removing anything. However, it was a huge pain, and would be a whole lot easier with the airbox off. With the airbox removed it shouldn't be difficult at all. The hardest part is getting the new retainer clip in without dropping it. I HIGHLY suggest tying a piece of fishing line or thread to it so if (when) you drop it you can just pull it back up and try again.

[Other_Erik]

Fixed here, no need for a new sensor for me.

Had a shop do my Timing Belt/Thermostat/Water Pump about a month ago, seems they left me almost a gallon low on coolant. Topped up, burped air out of system, topped up again, etc... Then ran the scan, cleared the code, no problems.

If only I could as-easily fix the "Brake Light" warning - replaced my high-mount incandescent bulbs with LED bulbs for much brighter brakes, now brake light warning on constantly :\

[Dmb408]

the trick with getting the new retaining clip in on the coolant sensor (just responding since that was brought up here) is to get one side of the clip going and then as you are pushing on the top of the sensor with a lot of weight...rock the sensor to the other side to give that side more room to get in while you leave the side you began with's plastic wedged as leverage then when both are started clear of the brass ring it will go in easier...i know from screwing this job up too many times.

[mrdave]

Just following up on an older topic. It's about 45deg F and I had a leisurely 30min drive home this evening. I noticed my coolant temp gauge was reading low but that's nothing new when it's chilly outside. What was new today was that I usually don't have that long of a drive and when I got home the fans came on full blast and stayed on after I parked it in the garage and turned off the engine. I pulled codes and got P2181 - 18613 Malfunction in cooling system.

After reading through this thread I'm now reasonably sure this error is caused by the engine running for a certain period of time (and/or speed?) but not reaching an appropriate operating temperature. The ECU probably assumes that if it runs for X minutes but still isn't at normal temp that there's a coolant system failure and then sets the code and triggers the electric fans. Anyway, I probably won't do anything to fix it for now other than resetting the code and making sure to replace the thermostat when I do the timing belt next time.