G8RB8

I overlooked the grounds, but everything else checked. Replaced relay 4. I have voltage at the plug for the final stage. I already put it back in the barn so I'll check the grounds later this week.

westside oz

So I'm new here but have the no fan power issue. Reading the very good explanations above I've so far got left fun power using a jumper but no right fan. I suspect a bad fan though as I heard a little click like a local relay maybe when I pushed the jump wire in to the plug. So I might go looking for the finned gadget on fleabay

dr bob

Westside:

Do follow the full diagnostic list before spending on parts. While there are cases of the final stages module failing, much more frequent are primary power issues with wiring from battery up to that module. The current load for the fans is high, so all voltage measurements need to be taken with everything connected and trying to run. It's easy to spot voltage with a DMM with resistance in a connection but no load on the circuit. That same resistance can cause significant voltage drop when load is attached. I like to use a 'needle' probe on the meter to test at the test port on the fuses, and in the back of the harness connectors to the CE panel while everything is connected.

Good luck, and please share your results.

FredR

Not that it makes much difference as all fan equipped 928's are pretty much the same in that department, but as a new member it is always a good idea to advise what model year you have as one finds that often there are minor differences here and there.

Fully agree with Dr Bob on the approach. Motors do go south quite regularly nowadays but that is far from the only failure mode possible. Cables can get damaged and the smaller connections on the positive post of the battery [one of which carries current to the fans] often look like a dog's dinner by now.

Rgds

Fred

westside oz

Noted, Fred. My mistake sorry. This is an 88 S4

I was poking around in the space shuttle's fuse panel yesterday and noticed that they have moisture a corrosion on the tangs. I think I will devote a part of my life to removing and clean all the fuses and obviously try and find the leak that caused that corrosion. One thing leads to another right?

Thanks again for chiming in folks. All advice will be taken

Dean_Fuller

Blower right above the fuse panel will develop leaks at the seal. Remove and reseal will most likely fix the leak.

dr bob

Following on Dean's recommendation, the blower box drains via a rubber scupper flap in the firewall. The area gathers leaves, pine needles and other junk, particularly if parked outside a lot. Make sure that flap and the area immediately upstream are free of debris so the water drains there rather than through the fresh-air flap into the CE panel and passenger footwell.

FredR

No apologies necessary- you are among friends.

With these cars at the age they are one thing precedes another- it is a never ending labour of love as it were and you must be prepared for that. Deal with it correctly and these cars are very rewarding but they are not a cheap proposition to keep in tip top shape and what most of us on this list strive for is to optimise our expenditure profile. Full membership is not very expensive but be assured it will pay for itself many times over.

The 928 is very quirky with some very advanced [for its day] features and some that seem monumentally dumb but it is what it is.

The fan system is only needed for idle and slow moving traffic type conditions, once you get some steam up the air blast does the rest. The electrics are often perceived to be the "Achilles heel" of the car to some extent- arguably unfairly. My engine harness started falling apart- most of it now replaced.

If the central electrics have been degraded then for sure you need to sort this out by pulling the relays and modules and cleaning all contacts with products like De-Oxit that are well appreciated on this list.

Different environments also play a role. Over here the underside of my car is something like close to new- in the UK they are in a terrible state. On the flip side my rubbery items get a hammering in our heat- batteries last a couple of years and tires 3 years generally speaking before the heat gets them.

Good luck with your quest.

Fred

dhubbard

Guys, I've been troubleshooting a similar issue on my '90 GT. The radiator fans don't kick in when I turn on the ac and the ac doesn't blow cold and the fog lights don't turn on. I tested the relay and that seems to be fine. While looking closely at the fuse box today I realized that fuse 6 (where the fog light fuse would be was missing), but worse appeared burnt. I've attached a picture.
I guess my questions are:
1. Would this fuse cause any of the other problems mentioned above?
2. How does one repair something like this without replacing the entire fuse panel which seems like it would be a nightmare.

Here is a photo.



Fuse 6 location melted

Thanks,
Dustin

G8RB8

https://rennlist.com/forums/928-foru...line-fuse.html

dhubbard

Thanks.

jwbeck17

I'm going to resurrect this thread, as when I was analyzing my weak AC (refrigerant pressure low) I noticed a few other issues that may be contributing to the issue as well as creating others.

I noticed that my passenger's side cooling fan was not running, while my driver's side was turning on and off. I ran into this issue before and it required a final stage replacement and I also had replaced the original passenger fan before over the past 8 years. Seeing this is happening again, I have started to follow the diagnostics that Bob listed here, and am looking for suggestions from you experts. Here is what I have noted so far:

-- Test for voltage at fuse 28 and 29 in the panel: I set the car to run, used my multimeter, connected the black to ground, and used the red to touch teach two pin tops of Fuse 28 and Fuse 29. No power. I compared it to a live fuse and confirmed that I was measuring correctly.

-- Connect the two wires hat are normally on the intake temp switch, top of the intake manifold: I performed this test with a brick on the hood button and jumpered the two manifold connectors. Drivers side fan went on low and continued to run. Passengers side fan went on low for 10 seconds, then stopped. I saw no voltage measurement at the fuses when testing.

-- VERIFY that the round plug on the "fan final stages" module is plugged in securely: I had removed and reinstalled the round connector several times, as well as added a drop of Deoxit to ensure clean connection

-- VERIFY that the wiring on the fan console is routed correctly, and that there is no damage to the wiring: I checked this manually and this looks good. the wiring is pretty fresh as I believe I had replaced it about 6 years ago with with a fan harness built by Sean. While possible for my soldering connections to be shot, the connection has been well sealed and movement does not affect the performance of the fans.

-- Pull and reinstall the harness connectors to the fan motors themselves: I unplugged and replugged them back in to ensure nothing got loose.


Based on these diagnostic tests, I am not seeing power to the fuses, so there may be something awry somewhere. Any thoughts on next steps?

Shark2626

You can put 12v and a ground directly to each fan to test if they are working or not, they should each come on at high speed when you do that. If one or both doesn’t, that fan is bad.

Mrmerlin

before you do any testing to the fans system ,
check and clean the battery terminals and the 2 wires bolted to the hot terminal. .

REPLACE both fan fuses with new quality fuses.
Put deoxit 100 on the fuse blades verify that the fuses fit with drag to indicate a solid connection
Replace the X bus relay
put deoxit on the fan connectors

Alan

The feeders to the top of those 2 fuses and to other things are connected direct to the battery lug positive. Disassemble & clean those and do what Stan says above...

Alan