Please can you help,

I have a 2003/4 porsche cayenne S
i have read lots of other threads where this fault has been solved by a new fan. this isnt the case with my fault -
A few months back my cooling fan 2 failed (always on, even if I pulled fuse 2 at night and replaced in the morning the fan would ramp up again) and brought up fault P0481 fan 2 control circuit.

Porsche replaced my fan and all was well for a few months. Then whenever my engine was turned off the fan would ramp up for 30-40 minutes non stop.
I returned to Porsche and they replaced the fan again this time under warranty.
This time it only lasted a few hours before it again stays on for 30-40 minutes when the engine is turned off.

A bit of background info – the outside temp here in the uk is 0-10 degrees so very cold and even if the engine is started quickly after not running for a day then turned off the fan starts ramping up as soon as the engine is switched off.
So the engine is stone cold!
The fan does not run while the engine is running. And it runs constantly for 30-40 mins no matter what the engine temp or outside temp is.
fault displayed has always been p0481 and is still the same now.

porsche say the fan is now definately ruled out they will have to investigate further but charge £144 an hour and have no idea how long it will take.

Anybody have any ideas?

thanks in advance
Leon

 

Sorry to hear that - nothing specific comes to mind. The P-dealer would have access to the best diagnostic protocols, so it is probably already in the best hands.

Just a suggestion, but you might want to find a reputable indy mechanic to take a look for a much lower diagnostic rate per hour. I would give them something like 2-4 hours to try to figure it out. If that turns up nothing, then I would take it back to the dealer and hope for the best.

 

For reference, here's a little breakdown of how the cooling fan circuit works on the 955:
At a coolant temperature of 93ºC based on the output of the coolant temperature sensor (or when the A/C is switched on), the DME sends signals to both fans to turn on. Each fan has an output stage built into it. The output stage controls the speed of the fan based on vehicle speed and temperature inputs from the DME.
Fan run-on is controlled by both the DME and the output stage, and turns the fans on after the engine is shut off, based on coolant temperature (90ºC+) and fuel consumption of the last drive cycle (how hard you were driving it). Fan run-on should be between 15 seconds and 13 minutes.
Failure of the output stage is common, and can cause the fan to run without DME input. This is what your dealer thought was happening, and why they replaced the fan, which comes with a new output stage. The next thing to check is your coolant temperature sensor. If your sensor is reading high, it could be kicking the fan on, or if it's not reading anything, it will kick the fans on as a failsafe. This shouldn't give you a fan circuit fault, but it's still worth checking.
If fan run-on is lasting more than 13 minutes, or if your temperature sensors are reading accurately, then your output stage is faulty (yet again), or it's receiving incorrect inputs from the DME, which means you'll need to check your wiring for shorts, and possibly replace the DME.

 

thanks for the replies renaissance.man and XR4Tim
XR4Tim - thanks for the great info thats all very interesting and will help me out a lot.
i think the temperature sensor should be ok as it is LPG converted and the LPG kit uses the coolant temp sensor to tell it when to switch from petrol to gas. this is always very consistent. (i think this is how it works)
im wondering if the LPG conversion is affecting it somehow? confusing the MPG reading making the DME think i have driven it hard as you mentioned and then kicking in the fan? or the piggy back ecu of the LPG kit affecting the DME readings? maybe im just thinking of anything that isn't the DME as im sure that will be very expensive!!
i have been recommended a local indy so will pass on your great info and see what they come up with

 

I don't see how the LPG conversion could be effecting the fan operation but you've now introduced another variable into the mix. What other modifications have been done? Electronics on these, and most complicated cars, are very interconnected and one modification or change or addition or elimination can cause one or any number of gremlins.

 

Hi denversteve,
Only other electronic mod would be my dension gateway but this is very recent and the fan issue has been ongoing way before. All other mods are cosmetic
I have tried running the car just on fuel without switching to LPG and there is no change in fault. Fan still starts up after engine is switched off and runs for 30ish mins. Ill get in touch with the lpg installer to make sure there is nothing he could have tapped into that could affect the fans