FredR

The S4 fans do not necessarily need to run on when the motor is switched off. There is a temperature switch mounted on top of the inlet manifold- if this detects heat above a certain temperature the fans run on until the temperature drops . If that condition is not met the fans do not run on. If the switch is not working correctly that might explain why the fan does not run if a condition exists where it should but I am not 100% sure of the default condition.

Mrmerlin

I would suggest that you disconnect the battery and clean the terminals and every wire thats attached to them,
NOTE the two red wires on the hot post power the fans.
Put deoxit 100 on all of the fuses,
pay attention to the fans fuses 30 ampers.

If either one fits loose in the slot then add a coat of solder to one side of the fuse blade and refit.
this indicates that the holder has gotten very hot and has spread.
NOTE its easier to fit a slightly wider fuse than to try to close an open socket in these fuse panels.

Remove the temp switch on the top of the manifold and check its operation ,
it should be open till it reaches about 240F use a heat gun and IR gun to verify temps.
A continuity meter will tell when its closed.
Replace it if any doubts or if it has gotten wet.

Replace the hood switch if any doubt about it working perfectly.

Open the front flaps at the motor twist **** under the rubber boot, and pull the fuse, this will keep your fans open.
It was a dodgy system and was eliminated after a few years in service.

Replace the coolant cap , the thermostat and the rear seal to it, and the heater control valve and short hose and the coolant.
Inspect the hoses where they fit to the water bridge for inside damage from the mounting area.

Test the temp 2 sensor and the the temp sensor,
verify the connectors are good,
replace anything thats perfect.

Clean the fan connectors, add deoxit,
and pull the harness to the finned fan controller and add deoxit to the pins,
do the same to the 14 pin connector at the hot post and clean the hot post wires as well

Bertrand Daoust

+1 what Fred and Stan said.

Also, first, there is no 92 S4.
91 S4 or 92 GTS.

Second, if only one fan is running, that's not normal. Both fans should be working all the time. At low speed or high speed. Depending.
It will run hotter with only one fan. But, again, something's wrong somewhere. Sorry but don't remember exactly what the problem might be.
There's a lot of thread on this (one fan running).

Mrmerlin

if you follow my instructions you should have both fans running when your done

FredR

Missed the bit about one fan running so that suggests an issue on the one that is not running.

The system detects if one fan is out and when that is the case it drives the operational fan at full volts to maximise available effect. In the UK climate probably not an issue operating temperature wise in slow moving traffic - my daughter was talking about having to use the central heating at home in the south of the UK this evening!

gunboot

Gentleman thank you very much! Stan I will do all that I saw the post a couple of years back about the grounds and deoxit and have used it ever since also I’ve ordered a new radiator the one that’s on does look a bit tired and I wouldn’t trust it on a long journey. Whilst it was being painted I cleaned the grounds I also had an electrician remove all the old alarms and immobiliser’s 6 in total miles if dormant cable and he tidied up the fuse board one thought that’s always been on my mind is the fuses I know about keeping them clean and deoxit but are there good quality fuses available on the market? They all seem to be the same probably made in China not that I have anything against China but if a quality alternative is available I’d rather use them.

Nige

gunboot

Stan I've done most of what you said cleaned all the earths cleaned the connections on the hot post replaced every fuse with new and put a drop of Deoxit D100 on them same with the connection to the fan controller checked the temp switch on top of the manifold disabled the bonnet switch temporarily now the opposite fan is running and the other one has stopped. The cooling flaps appear to be working ok I'm not sure which fuse to pull I did a bit of research and found in another thread it is number 24 15 amp but this didn't stop it closing so must be wrong. I've had to drive it to the upholster's today it drove fine no overheating although I'm not convinced its right! The heater valve must be stuck in the hot position as the cabin got very warm I will continue with the rest of your fault finding tips and replace the radiator when she comes back and let you know how I get on.

Bertrand you were right I have done a bit of research and my S4 was made November 91

Thanks again

Nige

dr bob

Nige --

A November '91 production car would be a 1992 model year. Porsche held off importing '92 cars to the US because there was a significant carryover still sitting at dealers. US owners aren't used to seeing 1992 cars, but they were manufactured and sold just not here.

gunboot

Thanks for clearing that up Dr Bob and I know exactly what you mean about a Beagle Puppy!


Nige

giddyupp

Seems to me if one fan was working and now the other one is - its probably something to do with the Final Stage Module and or the wires that run from that down to the fans. This is the finned electrical board that sits at the nose end of the car, right where you open the hood/bonnet. These are known to go bad. You can check power going into it, then figure which wire goes to which fan and then check power out to each.

gunboot

Thanks for that I did check the plug on the final control unit like Stan said I was surprised at how bright the pins were no corrosion at all that said I it could have failed internally. The car is at the upholsterers now so I will look into it a bit deeper when it’s back and let everyone know how I get on. I’m sure I will be asking lots of questions in the near future I have owned the car a long time but decided to have it resprayed and the interior tidied up as such she’s been off the road two and a half years I’m now at the stage where she’s been MOT’d and back on the road but I’m sure there will be some gremlins to sort out.

many thanks Nige

Shark2626

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dr bob

There's a temperature sensor on S4+ cars, mounted in the front bottom of the radiator immediately opposite the lower hose nozzle. The sole purpose of this sensor is to tell the fans-n-flaps controller when the engine cooling is ready for some fan operation. If you unplug the sensor, (from feeble memory...) the fans default to a mid-speed run state while the engine is running (key in run position) via the X-bus relay close.

An easier test for basic fan function is to depress the hood switch with hood open, then connect the two wires at the intake temperature switch. Key off, this tells the fans-n-flaps controller that the intake is too hot, and runs both of the radiator fans at low speed. This is a lot easier than reaching down and blindly pulling the temp sensor connector on the radiator. For sure it's easier than blindly trying to get that connector back on.

Shark2626

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Shark2626

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