Cooling Fan Constant Run - 86.5
 

The cooling fan started to run all the time. I've searched the threads and done the following but can't find the culprit. Any thoughts on next steps ? Thanks !

Fan runs constant: Engine Off. AC switch Off.
I cleaned the fan wire connection
The radiator bottom driver side temp switch shows no continuity - good
The Temp 2 switch on manifold showed no continuity - good

Next ?

There is a temp sensor, not temp 2, that is screwed into the organ pipes on 85/6/6.5

It is designed to keep cooling fan running with engine off, if engine is really hot. You might check that connection or switch by pulling off leads, else, making sure one isnn't hanging off touching something.

That circuit actually runs the fan at lower speed than the radiator lower sensor circuit. It passes through a round ceramic looking resistor on passenger side, mounted to fender IIRC, up by the radiator.


So three things can drive the fan. AC circuit, radiator circuit, and at lower speed the above temp sensor. Only the temp sensor in the organ pipes will do it with key off. (unless you've got a total meltdown somewhere crossfeeding in harnesses-- hey, it happens)

I think later cars, S4, might also have a trans temp sensor that will run the fan, but the 86.5 doesn't.

Helpful, thanks.

Here's a pic of the temp sensor. The car is dead cold and it has no continuity, so that should be good. So where is the power coming from ? The problem just started, not that that means anything . . .


https://cimg7.ibsrv.net/gimg/rennlis...c4f7965000.jpg

No that's Temp II. Its installed in the water bridge and provides signals to the engine controller. Not in play.

Look up, back, I think towards drivers side --- of the air handling organ pipes.
You will find a temp sensor screwed into them.

I'll look for some old pics

Here's what it looks like on a S4.

Might be the same part on your MY. Don't know.

https://cimg9.ibsrv.net/gimg/rennlis...cee51ba2ff.jpg

https://cimg9.ibsrv.net/gimg/rennlis...5a675d78c1.jpg
Actually, I think it is visible in your picture 86.5 picture, look to the other side of the oil filler neck, its screwed axially into the intake. In my picture, its lightly circled in yellow.

Nice engine compartment Bertrand!

Thanks Landseer.

I think you mean this one. Right?

https://cimg3.ibsrv.net/gimg/rennlis...d9b2655e45.jpg

Seriously nice engine compartment - hope to get there some day,

Thanks for the direction - I think that did it. I pulled the connections and the switch is closed (i,e, there is continuity); And the fan runs when I jump the two wires.

Adding new switch to the order list.

So, looks like 3 temp sensors across the top/front of an 86.5 Temp 2 (feeds ECU), temp sensor from the cooling fan, what's the 3rd on the right side - pic below with blue wires?
Have a nice New Year.

https://cimg4.ibsrv.net/gimg/rennlis...6494686212.jpg

Its been a few years since I was last fluent in this, but am pretty sure that is water temp.

I think radiator sensor is just a temp switch.

It's called here a "Temperature Sending Unit".
It sends coolant temperature to the cluster gauge.

https://members.rennlist.com/v1uhoh/underthe.htm

There is also an inlet air temp sensor in the air cleaner housing.

^This.

One wire goes to the gauge on the cluster, the other goes to the warning light at the top of the gauge travel.

Is this the correct sensor/number ? 928-606-217-00

the fans will run off the intake air temp sensor, or if an auto, the trans temp sensor. if either one is "on" , the fans stay on.

Looks like it.
https://cimg1.ibsrv.net/gimg/rennlis...b29be0c963.jpg

https://cimg2.ibsrv.net/gimg/rennlis...8ab4dee4bb.jpg