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Cooling Fan Constant Run - 86.5

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Old 12-30-2017, 01:15 PM
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Ramp
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Default 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 ?
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Old 12-30-2017, 01:23 PM
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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.
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Old 12-30-2017, 02:01 PM
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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 . . .


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Old 12-30-2017, 02:17 PM
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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
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Old 12-30-2017, 02:29 PM
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Bertrand Daoust
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Here's what it looks like on a S4.

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

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Old 12-30-2017, 02:30 PM
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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!
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Old 12-30-2017, 02:59 PM
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Thanks Landseer.

I think you mean this one. Right?

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Old 12-30-2017, 03:00 PM
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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.

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Old 12-30-2017, 03:13 PM
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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.
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Old 12-30-2017, 03:13 PM
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It's called here a "Temperature Sending Unit".
It sends coolant temperature to the cluster gauge.

https://members.rennlist.com/v1uhoh/underthe.htm
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Old 12-30-2017, 03:17 PM
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There is also an inlet air temp sensor in the air cleaner housing.
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Old 12-30-2017, 04:04 PM
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Originally Posted by Bertrand Daoust View Post
It's called here a "Temperature Sending Unit".
It sends coolant temperature to the cluster gauge.

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

One wire goes to the gauge on the cluster, the other goes to the warning light at the top of the gauge travel.
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Old 12-30-2017, 04:28 PM
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Is this the correct sensor/number ? 928-606-217-00
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Old 12-30-2017, 05:09 PM
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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.
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Old 12-30-2017, 05:22 PM
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Originally Posted by Ramp View Post
Is this the correct sensor/number ? 928-606-217-00
Looks like it.


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