dazzak

Hi All,

Had a bad day today with the 928 (it's a Euro LHD 1991 S4). Apologies for the lenght but want to get across all that happened and see if anyone has any thoughts.....

I thought I'd be good and check fuses and then under the hood, clean/grease (as appropriate) various parts including any electrical connections. I had noticed a while back that I'd never heard the cooling fans come on / continue even after turning the engine off.

I checked all battery connections were tight and fixed as well as those to the fan control unit - all good.

Warmed the car up and got it to temp (around 85 degrees), fans kicked in as normal and I left it running for a while to see how high the temp got (about 89) which I believe is ok. I switched the engine off and then closed the hood and low and behold for the 1st time ever the fans came on while engine was off (success I thought). After about 25 mins I thought this can't be right! I then checked the radiator fan fuses and I guess because of the length of time that they had been running - 1 had melted a bit. removed both fuses and replaced but this time no fans came on. I started the engine again and got it to temp - still no fans at all.

Looked up Wallys HVAC guide and followed the troubleshooting section - As the engine is still hot right now I couldn't test the fans with direct power but I am assuming/hoping as they were working all week and today that they are actually ok (?!). I then got to the fan control unit - hopefully I interpreted them correctly as far as I understand where you check pins 6&7, 8&7 is the plug nearest the door/outside as this is the only one that has those pin combinations - unfortunately if this is correct there was no voltage there (although checking other combinations including the 2nd plug - nearest the floor - I did get 12.53V but assume that's correct due to the other live/ground wires that are there).

Do you think that it's the fan control unit or is there something sinister behind the fuse box to check - looks hard to get out with all that wiring!

At some point during all this the computer told me that anti lock was off and differential control was off - have put this down to me "stealing" a 30A fuse from positions 31/32 which are supposed to be empty plus replacing the ABS fuse. Plus!! radio stopped working but got this working again (looks to be a bad contact behind the radio and nothing to do with the other issues!)

Thanks all in advance,

Darren

dazzak

PS - been doing some more research on here (getting late though!) so tomorrow I will:

1 - Put together the 2 wires going to the temperature switch at the bottom of the radiator (with ignition on)
2 - Check the control unit fuse (fuse 36)

Believe you can also jumper one of the sensors on the top of the engine (with ignition off) - in the "What is it" there seem to be 2 sensors - 1 to the left which is a Temp II sensor (928 606 126 00) or one just to the right of that "Temperature Sending Unit (928 606 201 03). Am assuming it's the latter to jumper the connections together?

Thanks again in advance!

dazzak

Hi,

Have made some progress today with all the various resources on the net but final state of play is not ideal! I went through and checked everything again:

1) Changed fuses for fans and for fan control box. Then checked relays were in snug
2) Fans both work ok with direct power to them

So this is now what's happening:

1) As soon as ignition is on (or engine on) - both fans come on full power. Unplugging any of the "temp" sensors makes no difference (inc one on bottom of radiator)

2) with ignition OFF, when you depress the hood switch both fans come on slow - ONLY when the radiator sensor (bottom left of rad) is connected. When you disconnect it both fans stop.

Am very confused! Wondering if this is a sensor issue or a new fan control module needed for inside the car or a new final stage output?

Any advice greatly appreciated.

Cheers

Darren

Herman K

I had to replace a length of wire behind the fuse box and make by-pass fuse holders as mine got burned out due to overheated fuses. If you send e yr e-mail I'll send you detailed pictures later. Got to run right now.

Best

Alan

Darren

Do check the fuse to the control unit.

The fans should come on with ignition whenever the AC is on (except during starting). Is the AC on (recirc truns it on also)?

Sounds like its possible the rad temp sensor may be faultly - check it - when the radiator is cool is the switch conducting or not? use an ohmmeter

If the control unit is faulty the final drive may stay on the whole time.

The after-running of the fans should never last much more than 5 mins - even in the most adverse conditions. Pull off one of the intake temp sensor connection (right on top oif the intake) this should stop the after-running - if it doesn't there is a different problem.

If your cooling fan fuses melted there is a problem with the fuseholder/old fuse. How did the old fuse pins look - was there any corrosion or black marks. The same is likely inside the fuseholder - so though you replaced with new fuses - you may still have contact resistance issue (make sure you only use name brand fuses for replacement - to me this means Littlefuse or Bussman fuses - way more expensive than some but still only a few dollars and also way better quality).

Try cleaning the fuseholders as best you can... and monitor in future.

Alan

WallyP

With the ignition on, the fans are triggered by:
- Temp sensor in the lower corner of the radiator.
- Refrigerant pressure switch on the receiver/dryer.
- Temp sensor on the torque converter (if automatic).

If the ignition switch is off, the fans are also triggered by the temp sensor on the top of the intake manifold. The fans will run slower than normally.

The radiator temp sensor should have no effect when the ignition switch is off. If the fans are running with the ignition switch off, unplugging the sensor on top of the intake should turn them off, hot or cold. When the engine is cold, the fans should not run with the ignition switch off. If they do, the problem may be the sensor or the relay. If the fans stop when you unplug the sensor on the top of the intake, it is usually the sensor that is faulty. If they continue to run with the sensor unplugged, it is usually the relay.

The final stage doesn't usually cause problems.

dazzak

Thanks for the info Alan - have just remembered I have the WSM here too but looked for them too late on my pc!

Couldn't resist checking bits people have mentioned on here today so despite the rain went back out for 5 mins :-)

The AC is not currently working - found hole in the condenser last week which is being replaced later this week and regassed - I dbl checked and the AC button is not in (it does light up if I push it in).

Fuse to the control unit is good - new one in today for good measure.

SO when I went back to it this time - unlocked car, popped hood - pressed the hood switch down - nothing happened which was to be expected. Reconnected the rad sensor and again pressed the hood switch = nothing happened which is expected. Turned ignition on, both fans came on full. Turned ignition off= fans stopped. Pressed down hood switch = fans came on slow (even removed intake temp sensor at back of engine nearest airfilter = no effect). Disconnected rad sensor and pressed hood switch = nothing happened. Jumpered the intake temp sensor and pressed hood switch = fans came on slow (whooppe - something that should happen!)

Surely when I have the rad sensor disconnected the fans shouldn't come on full (with AC off) at ignition on? I am not too hot on electrics but I got the engine up to about 80C and used my mulitimeter set to 20K ohms and the reading I was getting was about .113 agree though it does sound like the rad sensor is also faulty anyway.

Is this possibly a relay or more I suspect a control unit? Wondering whether to order a used one from 928international? ($150 vs $350!)

Thanks all once again for your continued help!

Darren

dazzak

Thanks for the info Wally - it is indeed a strange one I am dealing with. I can't see how the rad sensor can stop the fans kicking in slow with the hood closed and ignition off. I've just responded with my latest findings to Alan in this post (should just be above this entry) so would appreciate what you think based on that.

You mention a relay - which one (Relay X?) I just have this feeling it could be the fan control unit :-( Is a 2nd hand one from 928international worth it or should just go for a new one (if that is indeed the issue part!)

Thanks

Darren

Alan

As I had noted the AC is also activated if you have the head unit in recirculate mode (regardless of the AC button position)... check that too.

However I did not think the controller would after-run unless the rad/intake was already hot - so in your test with cold rad & intake that still seems odd..

But as I think about it I'm not sure if there might be modes where that might happen... e.g. maybe it runs for a while to cool the condenser if the AC was on...

This time of year my car is always hot when I shutdown so it always after-runs for at least a few seconds.

Alan

dazzak

Hi,

No its definately not in recirculate mode (at least the sliding switch is pointing at the up/down arrows)...

At next available opportunity am going to do some of the WSM tests as they seem fairly easy to follow - even for me and take it from there. Just have this sneaky feeling it might be the fan control module by the passenger seat (plus probably a dodgy sensor somewhere!)

I'll see when the condenser is replaced later this week if that miraculously clears anything :-)

Thanks for your help and if you have any brilliant flashes of inspiration of what it could be then let me know.

Thanks

Darren

Hilton

With the sensor on the radiator disconnected, the fans default to full-on with the ignition on. Its a safety measure - the circuit is designed to ensure you don't overheat the engine if the sensor fails.

I find it's also a handy reminder to plug the sensor back in when you've had the radiator out

The excessive current draw on the fuses indicates to me that the motors are pulling too much juice. Have you tested the current draw on each fan circuit? Could be they need new bearings and/or brushes.

How corroded are your fuse and relay contacts, and ground points? My '87 came from the UK earlier this year, and I was amazed how much more corroded the electricals were than my '89 (which spent the laast 10 years in NZ, but was also originally a UK car). The damp climate doesn't help

Alan

No !! I know this seems intuitive - but its completely wrong... there is no excessive current draw... melting fuses has no implication of too high a current.... if the current were too high the fuse would blow - thats the simple inescapable fact...

Fuse blades getting so hot they melt the fuse body plastic (or fuse holder) is a sign of high contact resistance - only high resistance causes heat at this location. Resistance is usually caused by surface plating corrosion or poor mechanical contact. Once started it rapidly causes further deterioration - possibly irrepairable. Act quickly to clean the fuseholder as best you can and subsitute clean, high quality new fuses as quickly as possible. You may still need to replace the fuseholders to solve the issue...

If you have cheap Chinese fuses in your 928 throw them out and replace with quality fuses before this happens to you - this is not the place to save a few bucks - It really does make a difference...

Alan

dazzak

Going to continue the investigation on 2 fronts - the sensors, fan control module and then the fuses - type and contact.

What's best for cleaning up the contacts (in fuse holders) - any particular "tool" or "fluid"?

Thanks

Darren

dazzak

and one final question - what's easiest way to change out the rad sensor - from above or below etc (and any special after procedures?)

Cheers

D

danglerb

Contact cleaner, not saline solution from Bosch and Lomb, but electronic stuff usually in a spray can. I like CAIG products deoxit and others. Electronics repair places will have foam swabs, but plugging and unplugging while using the spray works too. I also apply electricians grease to the contacts once clean.

Sensor isn't too handy above or below, not bad with the radiator out though.