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1989 Seville
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Discussion Starter #1
I have a 1989 Seville. The coolant fans are not coming on. I get the message "Coolant Fan Fault" on the console when I turn on the ignition. The message will also appear while I am driving the car. I have tested the fans and when I apply power to them they work. I have removed the fan control module and took it apart. There is nothing obviously wrong inside (nothing burnt or blown). With the ignition on and the engine not running I disconnected the small lead (control lead ???) from the module and both fans started up. I connected a voltmeter to the leads and both contacts show ground with the ignition on and the engine not running. When I plug the lead back into the module both fans turn off.

I need some help finding out what the problem is. Can anyone tell me what to look for / test to find the problem?

Thank You
Bob
 

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'85 Fleetwood FWD
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728 Posts
According to my manual, if you enter the diagnostics, select cooling fans over ride (F.8.5) , hold the "hi" button (heater fan) for 30 seconds to get high fans.
The fans will be either on or off.
It's a two page flow chart, and difficult to put it all on here.
If they are "on", hold the "low" button to command fans off.
If they go off, hold the high button (again) to command high fans.
The fan status on the panel (auto fans) should come on within 15 seconds.

If the auto fan indicator comes on, hold the "lo" button to command fans off.
That fans status indicator should go off within 15 seconds.

Depending on wether it goes off or stays on (off is good!!) there's more tests.
 

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1989 Seville
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Discussion Starter #3
Thank you steelybill. I am able to enter the diagnostics by holding down the "off" and the "warmer" buttons at the same time. Would you please explain how to "select cooling fans over ride (F.8.5)". When I enter diagnostics it cycles through some codes (likely previous error codes) then displays "EMC?". I can get other options but I could not find anything resembling "cooling fan over ride".

Bob
 

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'85 Fleetwood FWD
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when you enter diagnostics, the system usually goes thru the segment check, then any trouble codes stored will be displayed. The pre-fix "E" will show up (with code numbers), and when it goes thru the E codes it will show F codes. When it gets thru all those it should read .7.0 on the display.
This is the decision point; For what we are doing;

depress and release the "econ" button (on the climate cont. panel).
The cooling fans override mode switches from the .7.0 display to code F.8.5.
to command Hi fans, hold in the HI button. The fans speed should increase until they reach max speed. To command fans off, hold the LO button. The fan speed should decrease until they are off completely.
If fans go off, go to my first post.

The trouble code for the fans is F41, if you didn't already know.

check it out like I said in the first post., and see what you get.
As you likely know , there are two computers here. the ECM, and the BCM. which is the one we are checking into (body computer module)

BILL
 

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'85 Fleetwood FWD
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If things get too sticky with this and other problems, you may have to get a factory service manual. I see that Helm Inc has them for you car. NOT CHEAP:bigroll: $105. But if it saves you just one trip to a dealer service place you are ahead of the game:thumbsup:
 

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1989 Seville
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Discussion Starter #6
When I enter diagnostics I get the following:

NO EMC CODES
NO BMC CODES
EMC?
At that point I can cycle through the EMC options or choose to go to the BMC options. If I select the BMC options "BMC?" I can cycle through them. One of the options is "BMC OVERRIDES?" If I select "BMC OVERRIDES?" there are 7 options
NONE BS00
PROGRAM NO BS01
VF DIM BS02
BULB DIM BS03
FAN SPEED BS04
129 OPTION 1 BS08
0 OPTION 2 BS09

If I select the option "FAN SPEED BS04" the value of 0 shows up in the upper display. I can increase that number by holding down the WARMER button. It will increment by 1 until it reaches 99. At no time does either of the fans turn on. I also checked the voltage of the 2 control pins on the plug going into the fan control module. They measure about 0.3 volts all the time, even while I am holding down the WARMER button during the "FAN SPEED BS04" option.

I am going to try applying some voltage to the each of the 2 control pins on the fan control module to see if that makes the fans move.

Bob
 

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1989 Seville
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Discussion Starter #7
If I apply a voltage to the input pins of the fan control module I can turn on the fans. If I ground the pins the fans turn off. Since I do not see any voltage change on the pins of the input plug to the fan control module I am guessing that the module is OK and the problem is elsewhere.

Anyone have any ideas where to look next?

Bob
 

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95 Fleetwood Brougham / 01 DTS / 11 CTS Lux / 11 DTS Platinum
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7,085 Posts
Cooling fan control module. It's located in the front of the car behind the grill on the passenger side. It's about $80 and will fix the problem.

Oops, I didn't read the whole post. I still think that's the problem or the coolant temp sensor in the manifold. That module is a pretty common issue for some reason.
 

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1989 Seville
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Discussion Starter #9 (Edited)
So how do I determine what the problem is? I would not want to buy a control module just to find out that it was not the problem. What is sending signals to the fan control module. Since I do not see any voltage change on the fan control inputs I would think that whatever sends the signals is not working or there is a bad wire/connection to the fan control module input.

BTW I get correct temperature readings on the console so perhaps the temperature sensor is OK.

Bob
 

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'87 Coupe DeVille 4.1L FWD(New engine '08) 1981 F100 '03FXDL
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879 Posts
If things get too sticky with this and other problems, you may have to get a factory service manual. I see that Helm Inc has them for you car. NOT CHEAP:bigroll: $105. But if it saves you just one trip to a dealer service place you are ahead of the game:thumbsup:
eBay is crammed with used FSMs. Years ago I bought a BSM for $6. FSMs are a little more expensive but much less expensive than a brand-new Helms. Helm is the publisher of most every OEM vehicle manufacturer service manual. IOW, the manual the dealer/tech refers to was published by Helm.
Anyone who works on their own Cadillac needs the Factory Service Manual. The FSM/BSM are tools. Any 'repair' manual is great for starting camp-fires, but they never have all the information needed...the Cadillac manuals cover every system in/on the car. When looking on ebay, input the year of the vehicle/Cadillac/manual to the search engine then look for your model Cadillac.
 

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'85 Fleetwood FWD
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728 Posts
Not sure how your car is set up. There may be another coolant temp sensor just for the computer. One of my Chevy trucks is that way.
At this point I'm inclined to think it's the module. I agree with Dave on the manual if you can scare one up on ebay. The fan control module may be available on ebay also. I bought a heater fan module on ebay for 30 bucks.

There are likely differences from my old '85 and your car, and trying to figure this out takes a while.
 

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95 Fleetwood Brougham / 01 DTS / 11 CTS Lux / 11 DTS Platinum
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Hmmm, I'm not sure. As far as I know the sensor in the top of the intake is the one responsible for the fans. There may be others but I'm not sure.

There are other inputs as well like from the AC to say weather the AC is on or not. If the AC is on the outside fan should run all the time.

I think there's more to it than that and I don't have any more details but I really think the module is the problem.
 

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'87 Coupe DeVille 4.1L FWD(New engine '08) 1981 F100 '03FXDL
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The control system for these 80s vehicles had problems. I've been chasing a ghost cooling fan fault for years. The previous owner described it, but there was never a problem associated with it other than the telltale coming on when the AC or Defrost was On. When in Econ mode, no telltale. The telltale would always go Off when the car reached 40mph. I chased down all the grounds/replaced the module 2x/replaced the coolant sensor/t-stat/etc, all to no avail. Recently there was a thread from a guy asking about the value of a cherry '87 Coupe Deville. That vehicle had the exact same bad behaviour problem mine does. I installed a coolant temp gauge just to make sure of the coolant temp and also to moniitor the cooling fans. My telltale still behaves as it always did, but the fans do what they are supposed to do. It's a 'glitch', prolly in the BCM, but it ain't broke so I ain't gonna fix it....anymore.
 

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95 Fleetwood Brougham / 01 DTS / 11 CTS Lux / 11 DTS Platinum
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Yes, correct. I'm aware of that problem. That telltale comes on when the BCM thinks the fans should be running and they're not. The system was a little to sensitive and threw the error before the fans had a chance to start up.

That's a known issue and if that's what your chasing, don't bother. If the fans are coming on when they're supposed to then you're ok.
 

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'85 Fleetwood FWD
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728 Posts
I believe my fan module has smoked itself into the "always on" mode. Fine. I can't find a replacement anyway. They run all the time, for the past two years.
Fixing all the grounds is a good idea. They are all over the car. The manual lists/show them all. What a way to build a car!! I went through the whole mess of them.

BILL
 

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1995 FWB 128,*** miles
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If things get too sticky with this and other problems, you may have to get a factory service manual. I see that Helm Inc has them for you car. NOT CHEAP:bigroll: $105. But if it saves you just one trip to a dealer service place you are ahead of the game:thumbsup:
I see a lot of FSM (Factory Service Manuals) on eBay for about $20. Nowadays you can find more FSMs on eBay than Cadies of that year.
 

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'85 Fleetwood FWD
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728 Posts
That's actually great news. I still have a '76 DeVille manual from when I owned one, and manuals for the wife's '93 Fleetwood, and of course the MOST used one, for the 4.1 '85
The manual for the '76 is handy since I built a 500 engine recently.

Maybe I can find a factory manual for my S-10 on Ebay.:cool2:
 
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