Dean_Fuller

Just got my 89 back running and noticed yesterday the car was getting hot in traffic. Got home and noticed the fans were not running. This is what I have done....

Cleaned extra wires at poss post on battery.

Checked fuses 28 and 29...both GOOD.

Checked voltage at both fuses..both have 12 volts.

Checked voltage at both plugs to fans..NO VOLTAGE.

Cleaned ground points.

Where do I go from here?

I have read something about fan controller??? What and where is that???

Thanks

mfitzgerald928

Hey Dean,
I had the same issue that I just solved by replacing the fan control box. It is a black finned box in front of the radiator on passenger side. Black plug on top. You can jump pin 1&5 and passenger fan should work. Jump pin 4&8 and driver fan should work. Paid $95 for a used one on eBay. Works perfect!
Mark

borland

WSM covers troubleshooting the radiator fans. Could save you from buying unnecessary parts.

MainePorsche

Pin 5 - red/yellow (+) to passenger fan (from fan control unit)
Pin 8 - red/blue (+) to driver fan (from fan control unit)
Pin 1 - red from fuse 29
Pin 4 - red/white from fuse 28

This is a temporary fix.

rbrtmchl

Dean, this may sound like a stupid question, but do your fog lights work? I learned a week ago that a faulty Ignition-X relay caused my radiator fans, fog lights and air conditioning to not operate. If you are having these symptoms, replace your Ignition-X relay. I think it is in position IV in your '89. You can try swapping in your horn relay to see if this restores your radiator fan operation.

dr bob

The "control box" lives in the compartment next to the passenger's seat. The "final stages" module lives in the front apron.

MainePorsche

Dr. Bob,
You're right. I had erroneously called it the 'fan control unit'. It is actually called the Blower Final Stage.

Dean_Fuller

You sir are steely eyed missle man!

Noticed my non working driving lights. Swapped relay IV I think. ( Ignition relay) with the twin horn relay. Horns have aways and still work. After the swap...driving lights are back and the fans kick on as they should. Who would of thought that relay has anything to do with the fans?

Thanks!!!

dr bob

Dean--

What work have you done on the car lately, at least since the fans last ran correctly?


You've done the basic stuff like clean and tightene all the connections at the battery positive post. Process continues with:

-- Test for voltage at the fuses in the panel. Thes are 28 and 29 for our cars. The fuses have small opening in the back that let you stick a meter probe in and test voltage at the top of the blade with the fuse installed. Should be battery voltage, referenced to chassis ground on bothj pins of both fuses.

-- Connect the two wires hat are normally on the intake temp switch, top of the intake manifold. This switch normally causes the fans to run on low speed with the key off and hood closed. So key off and either the hood closed or the switch taled down. Fans should run on low speed. Repeat the votage check at the fuses. Should still be full battery voltage referenced to chassis ground. Low or no voltage on any of those fuse points means there's a fault between the fuseholder and those smaller wires at the positive battery terminal.

-- VERIFY that the round plug on the "fan final stages" module is plugged in securely. That little metal retainer arm swings out of the way, plug can be pulled and reseated a couple times to wipe the connecting pins.

-- VERIFY that the wiring on the fan console is routed correctly, and that there is no damage to the wiring. The harness sections clip into the frame with little metal Z clips. I supplement those in a few critical places with small cable ties. Wiring needs to stay completely clear of the fan blades, the drive belts, and the lower radiator hose. where it's tied to the saddle on the fan console.

-- Pull and reinstall the harness connectors to the fan motors themselves.


Besides those steps, there are some electrical faults that might affect the operation of the fans.

-- The hood switch is part of the fan control scheme. WSM says that the hood switch will cause fans to stop when the hood is open. In my experience (my car only...) this protection is only afforded during the intake and auto trans overheat modes.

-- The radiator temp sender (described as a switch in WSM wiring diagrams) needs to be plugged in for fans to work. Front bottom of the plastic tank on driver's side of radiator on US LHD cars.

-- The fan "final stages" module seems to be the more fragile of the two electronic modules. Failure typically results in one of the fans not running correctly. It's possible that both independent channels in that module have failed. so don't rule out that possibility. Best/only real diagnosis is to pull your module and plug it into another S4+ car, see if it runs the fans the same in that car.

-- The controller module next to the passenger's seat lives a perfect life. Covered, shielded, on a climate-controlled environmnet, only sees low-level signals from a dozen different places. I've heard of only one or two failures of this module. But it could happen.

-- Controller and signal power come through different circuits than the motor power mentioned above. Fuse 3 protects part of the controller, routed through the X-bus relay. The controller also gets full-time power from the 30 bus, with no fuse protection at all. So fuse 3 and the X-bus relay (in position 4 on the CE panel) would be good places t look. You can do the same in-service power test through fuse 3 that you did for 28 and 29 above. However, the X-bus is only energised when the engine is running. (Key in run position 3, starter not engaged). So check that fuse with key on at least. As others have suggested, that X-bus relay powers the fog lights and other things like HVAC blower, so easy to check the relay by checking for fog-light operation. It's a standard 53B relay so replacement as a PM task isn't a bad idea.

-- HVAC fans, controller module and final-stages module all ground at ground point MP-II. It's an easy one, on the right side front just forward of the AC condenser and inconveniently under the headlight crossbar. Weather-exposed there, it's a good candidate for regular cleaning and resealing. Do the one (MP-III) on the other side by the ignition final stages modules, and the one (MP-I) on the fender wall just forward of the jump post WYAIT.

Dean_Fuller

Thanks for this...I jumped as you said and the fans worked...so I knew my problem was not from that point back. That help. I ened up swapping relays and I got my fans back so glad I did not have to replace the finned part...but it may be going bad.

dr bob

Hmmm--

Was typing while you were reporting the fix results. Excellent!!

Dean_Fuller

Thanks for all the tips...you sir are also a steely eyed missle man.
Just following up so others will have a completed tread to reference.
Thanks again to all that relied.

G8RB8

I jumpered the pins on the final stage module and the fans still don't run. Can both fans be bad?

crushingday

Always great to see a thread that states: FIXED

dr bob

Did you start at the beginning of the diagnostic list? Jumpering the connector at the final-stages module only works if the fan feeder connections at the battery positive are good, fuses 28 and 29 are good, fan motor grounds are good, and the fan motors are good.