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Jake
Jake, Automotive Technician
Category: Porsche
Satisfied Customers: 3646
Experience:  Experienced collision repair technician, Pulaski Tech graduate and DSM hobbyist.
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2008 CAYENNE 3.6. I replaced cooling fans because the wires

Customer Question

HI. 2008 CAYENNE 3.6. I replaced cooling fans because the wires going to the electronic units on it corroded away. Now the fans will not stop even with the keys removed from the ignition
JA: Have you checked all the fuses? Do you have a wiring diagram?
Customer: i did. 60 ,30 and 10 amp fuses ok
JA: Are you fixing your Cayenne yourself? What have you tried so far?
Customer: yes i am. i have the wiring diagram
JA: Anything else you want the mechanic to know before I connect you?
Customer: no
Submitted: 3 months ago.
Category: Porsche
Expert:  Jake replied 3 months ago.

Hey there, thanks for the question.

did you make sure the connectors were seated properly? I have seen connectors that are corroded or damaged cause the fan modules to make them run randomly or continuously.

otherwise you could have an issue with the temp sensor on the passengers side of the block.

let me know how I can help further please.

Customer: replied 3 months ago.
Hi Jake, the connectors from the car are OK. Is the sensor located on the housing of the thermostat?
Expert:  Jake replied 3 months ago.

If i recall correctly its underneath the passengers side of the intake manifold. Tight little spot of course.

I know some touregs and "maybe" the cayenne too has a fan switchseperate from the actual temp sensor ad its on the radiator water outlet.

Customer: replied 3 months ago.
Hi Jake. I spotted the sensor on the water outlet. What should be the resistance of this sensor. Also do you have a wiring diagram that could help me. I'm using Mitchell and it doesn't even give me the locations of the sensors. Thanks
Expert:  Jake replied 3 months ago.

Hey, sorry for the delay.

I don't have any meter specific testing documentation. Testing would be done taking a coolant temp reading and looking at the live data stream from the temp sensor switch itself.

Customer: replied 3 months ago.
Hi Jake. I checked with my scan tool and temperature from sensor is OK. Which sensor tells the fans to switch on? The one on the thermostat housing or the one on the rad inlet pipe. Thanks.
Expert:  Jake replied 3 months ago.

Technically the answer would be both of them.

The one on the radiator inlet pipe is what tells the fans to run when the engine is off, the one on the thermostat housing is what tells the computer engine temperature and regulates by operating the fan while driving/idling/etc.

Customer: replied 3 months ago.
Changed both sensors and still the same. Do you think it could be a bad ecu??
Expert:  Jake replied 3 months ago.
Theoretically yes, but based on experience that is very unlikely. Did you replace just the fans or the fans and the modules?What was the problem with the old fans other than the corrosion? Did they function at all?
Customer: replied 3 months ago.
The expansion tank and rear hose assembly blew so i replaced them. Then i realized the fans were not working so i replaced the fans and modules as an assembly. Can't be sure if the original fans were working before but I'm sure they weren't and that's why the expansion tank and hoses blew. Now I get 12 volts and ground on the large wires at the fan connectors and ground on one of the small wires when the car is off. That small ground wire becomes 12 volts when the car is turned on. The last small wire is a data signal when the car is turned on.
Expert:  Jake replied 3 months ago.

is the large wire staying to ground when the engine is on? or are the fans shutting off when you start the engine?

Customer: replied 3 months ago.
The large wire always stays on ground and the fans stay on all the time. Engine on or off doesn't make a difference.
Expert:  Jake replied 3 months ago.

if you can upload your wiring diagram I will be happy to look at it for you.

I don't have one here at home for it.

sounds like the fan module, was pretty common early on with these trucks which is why they started selling the module seperate from the fan assembly later on and issues the TSB, but you already said you replaced it.

Customer: replied 3 months ago.
Hi Jake.
Yeah that's what I thought but they're both new. This one is killing me. I don't have the diagram with me either, but Mitchell Prodemand is letting me down big time!! I really need to solve this issue. Any help would be greatly appreciated. Thanks
Expert:  Jake replied 3 months ago.

hey sorry, busy day :)

does the fan shut off when you start the engine? even thought the small wire is switching ground to power?

Expert:  Jake replied 3 months ago.

also, bizarre as this sounds - disconnect the fan module and reconnect it for me.

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