Doc GTO

I did a search but did not come up with anything.

When I turn my car off after driving it the cooling fans stay on and will not shut off until the battery is dead. I know that they should run for a few minutes and then go off so what do I need to check or replace t fix this???

It gets tiring popping the hood to kill the fans (safety switch) while out driving around when you have to park it . . .

Any help is appreciated!!!

My car is a 1987 S4 if that makes a difference.

ROG100

Try the temp switch on top of the inlet manifold. With the fans running remove the connectors. If the fans stop its the switch.
This would be an easy fix.

Doc GTO

O.k., does anyone have a pic of this switch location?

Thanks!

Sailmed

Here is a great start...
http://www.billsworkshop.com/P928S4/resources.htm

Then head down to Tony's Silver Bullet page.
If memory cells are still intact - you'll find it in the "Where is it located"

here

http://members.rennlist.com/v1uhoh/underthe.htm
Many thanks to Tony....

You're welcome

Doc GTO

Thanks guys! Went to the link and downloaded the info. I'll check it tonight!

worf928

Also, temperature switch in the bottom of the radiator front of left-side side tank.

bd0nalds0n

My vote is the temp switch in the radiator.

ZEUS+

The cooling fans will run after shutdown if coolant temp is above 85 deg C or intake temp is above 87deg C. A failure of either switch will cause this condition.

Pizza

Walley helped me with this. Hope it helps.

"On the '85 and '86 models, the electric cooling fan is operated by three (5-speed) or four (automatics) sensors.

A coolant temp sensor is located in the lower forward face of the radiator end cap. This sensor is open below the set coolant temp, closed above that temp. You can buy sensors with different trigger temps. To test the switch, pull the harness off, check continuity of the switch. Should be open when the radiator is very cool, closed when the radiator is above the trigger temp. To test the fan circuit, pull the harness off, turn the ignition switch on, and short between the contacts in the harness. The fan should run. If it doesn't, check fuse # 29 (25 amp) or relay XVIII.

A Freon temp sensor located on the stem of the receiver/dryer. This sensor is open below the set temp of the Freon in the receiver/dryer, closed above that point. Tests are the same as for the coolant temp sensor. This sensor does not appear to be very effective on most cars. It doesn't operate when the Freon "overheats", but when it gets hot enough to show that the A/C is operating.

A transmission fluid temp sensor is located on the torque converter, on automatics only. This sensor is open below the set temp of the transmission fluid, closed above that point. Tests are the same as for the coolant temp sensor.

These three temp sensors work by grounding terminal 85 of relay XVIII, triggering the relay. The relay contacts are fed from bus X (ignition on) thru fuse # 29 to relay terminal 30, and the output contact (terminal 87) runs directly to the fan, running the fan at full speed. The fan runs when any one of the sensors triggers the relay.

In addition, there is an air temp sensor mounted on the intake plenum. This sensor is fed power thru fuse #23 regardless of ignition switch position, and is open when the air in the intake is below the set temp, closed above that temp. When the sensor closes, power is fed thru a resistance to the cooling fan, causing it to run at a lower speed. This is primarily for cool-down after engine shut down."
__________________
Wally Plumley
928 Specialists

dr bob

The sender in the front of the radiator is in fact a temp sender, not a switch as descrived in a few places like the WSM electrical diagrams. With the multi-speed fans and the mult-position flaps depemding on coolant temp variations, it tends to point to how a swicth just wouldn't get the job done. And FWIW, that temp sender is ignored after the key is off.

So that narrows it down to the temp sender on teh top of the intake manifold is suggested by Roger, and can also be the tramsmission temp switch. Either of these switches can cause the fans to continue running after the key is off. The intake switch is a more popular cause and is easier to diagnose. As suggested, just pull the wires off the switch and see if the problem stops. The switch itself is easy to change since there's no coolant or other fluids to spill with the switch removed. If that doesn't cure the problem, report back for some more diagnostic steps with an ohm meter that can save you from sliding under the car to find the trans temp switch.

bd0nalds0n

I take it all back

ZEUS+

So the information from Theos site (last paragraph) is incorrect ?
http://jenniskens.livedsl.nl/Technic...3/MyTip331.htm

worf928

Troubleshooting electric fans: WSM 19.22 - 19.26

dr bob

I'm going by experience only with the few cars I've worked on. In my own car, while the intake temp switch was disconnected (due to failure caused by OFU washing the engine...), the fans did NOT run on when the engine was stopped following summer driving, the climb to my house on a hot day with AC working hard. It's quite possible that the AC was keeping the fans running, but the temp gauge at shutdown indicated temps warm enough to deserve the fans running if the engine had been running. Not saying that Theo's statements are not correct, only that I didn't obeserve that behavior in my own car during the week or so it took to get a new switch and install it in my intake. Dave C works on these all the time and might have good info to add. The WSM sections on troubleshooting don't appear to address this particular issue directly.

I do have a complete spare controller pair and connecting wiring, so one of these days I'll get a round two mocking up a system for demo/testing. That will be the easiest teaching/diagnostic helper I think. One of these days...

worf928

The WSM doesn't have much to say on the subject of why anything should or shouldn't happen with the electric fans - just go through the test points. Neither the WSM nor the wiring diagrams give any indication that one or the other of the temperature switches/senders/sensors will cause fan after-run. The logical implication is that if one of them will cause after-run so might the other.

I replaced that "temperature sender, cooling water", called a switch in PET, a couple of times. IIRC in one case the failure mode was that the electric fan never ran (this on a pre-87) and IIRC, on my GTS the fan ran all the time. It would be simple enough to test the permutations of the two sensors to determine if either one, only one, or both in combination can cause after-run.

There's no point in arguing. The main thing is to go through the test points and see if anything jumps out. If so, well then, there you are. If not, deeper digging needs to happen.