My cooling fans quit working on my '85 FWD Fleetwood. I have the manuals to trouble shoot it, but from what I hear the module is the likely culprit. I'm checking all the other components, like the diode, the fan relay, the grounds, and a fusible link in the circuit, etc. Someone mentioned that module here a couple months back, being for sale, but I don't remember where.
Of course the fans quit just after I fixed the oil pump and a pan gasket leak.......
I may have to hot-wire them to run all the time.
Run your codes to see if you get a coolant fans problem (F41). There is also a sequence you can run through the OBD that bypasses the module and tests just the fans. The quickest way though is to just turn on the A/C. Both fans should run when it's on. If they don't the culprit is almost always the module.
Don't hesitate to grab a module from the junkyard. I believe it's the same from '85 through '92. The module is slightly bigger than a deck of cards, with a finned aluminum top, and is mounted on the radiator brace, behind either the left of right headlight. You have to remove the headlight to get to it, but it's a plug and play swap. I put a junkyard part in mine 4 years ago and the fans have worked perfectly ever since.
It's not always the module. What are your symptoms?
Basic operation is that the BCM monitors the coolant temperature and the A/C high pressure temperature, and sends PWM power to the fan control module as needed. In turn, the FCM amplifies the power to the fans, monitors the current draw to see if the fans are going on/slow/fast/off when commanded, and reports those changes back to the BCM for oversight. Failure can be introduced at any of these points, IE bad wiring from BCM, a damaged FCM, bad fan motors, or bad wiring from the FCM back to the BCM.
If you have the FSM this info is scatter across four different places, but its the electrical circuit text that tells you the real story. The FSM also describes ways to monitor and test things but in the end you will have to watch diagnostics on the climate control panel to see what is happening. On my 85 DeVille with intermittent F41, the fans don't respond to high speed command quickly, the FCM sees current draw is not high enough and reports a failure. I am about to replace both of the fan motors since the originals are 26 years old now, which is a long time for an electric fan motor.
Rockauto still sells the AC Delco FCM module for my 85 DeVille and your 85 Fleetwood here, but can be found under Cooling System -> Radiator Fan Assembly. The modules are not the same for all of the years.
Sometimes there's an underlying problem that took out the module, if the module is even bad. That is an excellent description. Be sure everything is in good working order, especially the fan motors. Make sure they aren't drawing too many amps otherwise your new module won't last too long. I believe they are supposed to draw 13 amps a piece. I'm not 100% though.