Hi all,

I returned home after a 10 day trip. I forgot to put the Cayenne battery tender on before I left so I figured I may have a problem starting the car as my battery is a few years old......Anyway, it started right up.

However, when I got home I noticed the rad fan was on, and on shutdown it continued to run. In fact it ran long enough to drain the battery. I put the battery on charge for several hours. Unfortunately it didn't resolve the fan issue. Next step was to buy a new battery. With the new battery in all was normal but as I step outside the car the fan comes on and goes off several times........I hooked up the Duremetric and the fault I am getting is P0460 short to ground or open........I checked the connector at the fan, the wiring at the fan module, and the connector at the temp sensor, but I suspect I have a bad ground.

Does anyone know where the grounds are located for the fans? Or has anyone had a similar problem?

In the meantime I have disconnected the rad fan connector to save my new battery......

Bob

 

Being new to these as well maybe I can help partially. MOST fan circuits are based on a temp sender that once it reaches a predetermined temp closes the connection and basically connects it to ground (switches on the fan). Only way to tell would be to check the sending unit with an ohmeter (cold vs warm) and see what it registers, other than that you might have a ground connection that shouldn't be there (rubbed wire etc). Maybe someone that knows where the sending unit is located can chime in and help you out further, or correct me if I am wrong...

 

Thanks for the reply snzuloz.
I'm fairly new to water cooled Porsche's as well.....
Here is what I have determined so far.

In this case the temp sender is sending a temp reference to the DME and the DME will signal the fan to operate. I suspect that the fan is either two speed or variable speed dependent on temperature. As to why the fan runs with the car off I am not so sure, that's why I suspect I either have a short to ground or a missing ground in the circuit.......

Bob

 

It's quite common for the fans to operate even with the vehicle off (depending on engine temp), they just should not stay on and be able to kill the battery (timer in system?) I'm guessing the ecu or DME-stands for in english? has control of the speed requirements of the fan(s). If I had access to a wiring diagram I would be able to help out further, suspecting a bad temp sensor would be the most likely guess, have run across a lot of vehicles that use a combination relay/timer control on the fans that also fail and cause the same issue you are experiencing. I am curious now...

Troy

 

Troy,

The DME is the ECU in this case......or in english electronic control unit etc.. Don't you just love acronyms!!

I agree the fan should run on shutdown with a "hot" engine, but in this case even with a cold engine the fan runs. That's why I suspect a short.

I agree on the temp sender, but it could just as easily be the fan control module.....I'd change the temp sender on spec, but it's a pain in the *** as it's on the rear of the engine. I have been there before changing coolant pipes......

A friend who is an indy and knowledgeable on Porsche feels it is corrosion in the fan module. It is mounted on the fan support.....

Fortunately I have the wiring diagrams so I'll start wringing out the wiring. If you would like any diagrams just let me know, I may be able to satisfy your curiosity!! LOL

This was my first water cooled Porsche and I have to say the most interesting especially when it comes to electrical issues!!

Bob

 

So here's the update on this issue.

I changed the battery as I had it load tested last year at this time and it was serviceable but about three year old and I didn't want to take a chance as this is my winter car. I had hoped the battery was the cause, but unfortunately it didn't solve the issue. The fan started up in high speed (limp home mode apparently) immediately. My temp repair was to disconnect the fan at the connector on the fan support.

Yesterday I wrang out the wiring as per the manual with all grounds and voltages checking as per spec. The fan module was clean, with no signs of external corrosion. Unfortunately there is no real way to check it out further. For this fault the manual uses a lot of elimination processes. That is, connecting new units to ascertain serviceability....I didn't have a new units other than a temp sensor, which was OK.....

In doing the continuity checks I had the connectors off for the fan, module , and the DME. All looked good. The only thing I did find was the module connector wasn't seated properly. When reseated the fan operation returned to normal. So, that was the fix for this problem........

Brgds,
Bob