Porsche Enthusiasts Club Forum

Hi,
When I parked up last night I heard the fan running and was still on when I went out later but didn't think anything about it.

Went out to move it there (no fan on) and the battery is dead. Opened the bonnet (then realised battery in boot lol) but when I closed bonnet again fan came on. So with bonnet open no fan but once I close it, fan starts up

So looks like will need either new battery, battery charger or jump leads to get it started but that doesn't sort the fan problem.

Anyone any ideas?

Could be a faulty Fan Relay, contacts burnt and keeping it on? (had a similar recent fault fixed - dismantle & clean contacts)
Not sure where it is and why the bonnet affected it - unless the jolt of it shutting triggered it.

What model and year is you have again Barnsey?

Its an 1987 S4 Lee.

Just went to pull the fan relay out but the fan had stopped.

Will take it out and clean it tomorrow when there is some daylight. It's parked in the drive so pretty dark.

Hi Barnsy9

The behaviour with bonnet is correct - you'll see the safety button RHS which cuts power to fans when bonnet opens since fans and fingers don't mix!

If you have an S4 then most likely cause is failed air temp sensor at back of intake. You'll see it sticking up in centre of intake with 2 wires attached.

Pull either wire off the sensor. Hold down safety button as if bonnet shut (it's on RHS, close to that end of cross brace bar). Do the fans now run or not?

Adrian

Hi Adrian,
Thanks for the info. I was out looking for the sensor but couldn't find it. I am a bit useless when it comes to finding things in the engine. Could you be a bit more specific on its location please.

Much appreciated.. Gary

Gary as you look at engine from front of car, at top centre is a rubber cap about an inch wide. If cap is missing then you'll instead see top of a silver coloured shaft and a c-clip.

Anyway couple of inches behind that towards windscreen is sensor bolted into intake - resembles spark plug in shape and size. Has 2 spade connectors attached. Remove one and see if fan still continues to run.

Hi Adrian,
I found the sensor and removed one of the spade connectors but fan still stayed on. So decided to the AA a call.

He tried everything you mentioned and concluded the sensor is working fine.

I think we have narrowed it down to the fact I was trying the aircon out for the first time the day it happened and possibly it's sensor has jammed.

It might not be this but it does make sense. Has anyone else had this problem?

Gary

The fans will run whever aircon demanded, but will shut down if aircon switch ok when you turn a/c off.

If intake sensor fine then another possibility is failure of rad temp sensor bottom left of radiator. Has a blue Bosch connector. If not properly seated fans will run - check if it's loose.

Other possibilities are failure of fan power controller (black finned module front right close to bonnet latch, or the fan control unit itself (under carpeted hump next to passenger seat).

The wsm has good section on troubleshooting the fans. If you work through that you will find the culprit! John Speake (google JDS Porsche) sells them on CD and they are invaluable for 928 owners.