My 87 S4 cooling fans are staying on after the car is shut off. They Normally stay on for a minute, But they've been on for nearly an hour. THey go off when I pop the hood. I know this is normal for safety reasons.

Pulled wires from the temp sensor on top of the intake plenum, NO luck.

I ended up pulling the fuses and now they are off.

I can put the fuses back in and they will stay off until I flip the ignition to accessory position and back or start the car and shut it off again. Then the fans stay on again until I pull the fuses.

By the way, When the car is running the fans are at HIgh speed and when the car is off the fans are running at low speed so I can assume the Fan amplifier is working ,correct?

Could the intake temp sensor be bad? My temp 2 sensor was just replaced...

Any ideas?

 

There's a temp switch at the auto trans that may be causing your fan run-on. Parallel to the intake switch, you can test for that switch closed by measuring resistance between the two leads at the intake without crawling under the car. Low or no resistance means the trans switch is the culprit.

There's also the option that the trans really is overheated. Trust your sensors, but verify.

 

Thanks for the tip, The Workshop Manuals have some information, but seem to be more or less related to the cooling flaps, which have been disabled long before I got the car. I recently had some trans service done, Maybe something got mucked up there.

THe Manuals say that a fault in the system will cause the fans to stay on, but I can't imagine them staying on after the ignition is off.\

Thanks again...

 

Yes, I can confirm that - I had one bad fan, so the other ran from the moment I turned the car on, until I turned it off.

(turned out to be a dead fan, plus either a bad intake temp switch (928 606 217 00), or a bad hood position switch (928 613 173 00)...replaced both and works fine now)

 

Sterling--

My first-hand experience with the fan switch on the intake came a week or so after the engine got a little bath as part of an appearance refreshing session. Took that long for the water to migrate down into the delicate workings of the temp switch and convince them to stay in the closed position. Easy diagnosis-- pul one of the wires off the switch and the symptom disappeared. You can test the intake switch with an ohm meter, where an open switch is OK at normal temps, a closed switch at normal temp is a problem. New switch is the solution.

For auto trans cars, there's an overheat switch down there somewhere (need to look at PET...) but electrically it's in parallel with the intake temp switch. That makes diagnosis pretty easy.

 

I had the 30 or 45 min fan running after shutting the engine down and most of the time it ran down the battery.

Replaced the temp sensor on the intake (rear of intake on top) problem solved.

 

I did what Sterling Mentioned and popped the hood, Fans, of course, went off. Came back about 3 hours later and closed the hood. Fans are now off, drove the car fans now stuck on again.

If the intake temp sensor was bad wouldn't simply unplugging it shut the fans down though?

Right now the only thing that will stop the fans is:

A. unplug fuses
B. Pop the hood open
C. Unplug plug on fan amplifier

I need to sleep on this as soon as the UFC fight is over....

 

Matt--

Next time you have the fans running like that after engine shutdown, start off with checking to see if the intake really is too hot. Pop the hood, fans may stop if safety switch wiring is intact and switch is OK. Is the intake manifold pretty hot? You can check the fan switch itself with an ohm meter at this time. Pull the two wires, and check ohms through the switch itself. Should be infinite/open/megohms. When hot, switch will show continuity/low ohms.

Problems show up when switch doesn't really open when temp drops. Temp switch shows some continuity, enough to allow the little solid-state switch in the controller to close and run the fans. The ohm meter is your friend.

 

They did go off by them selves last evening after dark, when it was only in the high 80s here and the car was inside for a while and out of the sun. The switch seems to be acting overly sensitive to temp. I will go check with the OHM meter tomorrow at my workshop.

 

You'd think there might be a time that it would shut off as you wouldn't want to drain the battery. I never actually timed it. Usually give up and pop the hood or pull the fuse to shut it off before it'll get the chance to kill the battery. I'm going for a drive now. It's cool and over cast today. I want to see if the extreme outside temps we've been having has any bearing on what's happening.

 

Sterling--

No timer that I'm aware of. Intake cools down from fans running, fans stop.

Mine started with your symptoms, eventually got to where they seemed to just keep running. New switch did the trick. New switch is about 25% of the cost of a battery, and much easier to change. Also better than finiding out the battery is dead and you have to go somewhere. Change the switch.

 

I replaced the top switch and it fixed my '87 S4 5 speed.

 

I believe there is a timer for about 30-45mins built into the fan controller. I came across this related to parasitic current debug and there are cases where you need to wait up to this long to ensure all the fan controller drain has ended...

I believe the reason for the long delay was related more to the flap controller rather than the cooling fans - since they should cool the rad to an acceptable level quite quickly.... later models with no flaps/motor still have the same fan/flap controller...

Alan

 

I don't think so, the fan may not come on while the car is not running, try it with the car warmed up. Warm the car let it idle, pop the hood and hold the hood switch down., to keep the fans running then look at your fans.

 

Sterling,

It looks like you and I are in the same boat. I disconnected my leads to the intake temp switch and the fans kept going. I dropped the car off at My mechanic, I've too busy with work to deal with it for the next week or 2. I told him to get to it when he can get to it. So it might be a week, but I'll be sure to let you know what it turns out to be.