FAN switch A is located near the thermostat

FAN switch B is located where the upper radiator hose goes into the cylinder head

If FAN switch A is stuck "open" the cooling fan will not come on
If FAN switch A is stuck "closed" the cooling fan will run continuosly while the car is on

If FAN switch B is stuck "open" the fan timer will never come on
If FAN switch B is stuck "closed" the fan timer will run for 15 minutes every time you shut the car off

 

You are almost right.

I'm looking at the wiring diagram right now.

The fan control module gets power from all key positions.

The fans are not wired in line with the temperature sensors. The sensors are wired to the fan control module. The temperature sensor closes to ground when the temperature is above a certain value. The fan control module, depending on the input, will send power to the fan relay(s) to switch one/both of them on, so the fans will run to cool the engine.

 

And... I really thought that when the engine is running, fan-switch A will cause both fans to run. It's only after shutdown that one fan runs by itself.

 

I just spent a long time writing a reply and it was lost before I could post it. Here is the short of it

I think this:

Both fans can be turned on by the FAN switch A opening (grounding)

Both fans can be turned on by ECU pin A12 (FANH) - when A/C is on this pin in the ECU becomes an alternative ground point that is wired before FAN switch A.

One or Both (I'm not sure) fans can be turned on by the Radiator Fan Control Module when the car is off. This is done by controlling ground to FAN switch B. If FAN switch B is closed then the fan or fans will not run. If FAN switch B gets stuck open, the fan timer only lets it run for 15 minutes or so, and then closes the ground to prevent your battery from dying. Its a fail safe and if your fans are running for the full 15 minutes after you shut the engine off, its a dead give away that the FAN switch B is no good, or worse you have some major cooling problem.

The yellow and yellow/white wires that are coming out of the Radiator Fan Control Module ALWAYS have power with the ignition on, and the fan relay switching is controlled by turning grounds on or off. These are either turned on by FAN switch A that goes to ground, or ON/OFF grounding pin in the ECU (pin A12 FANH). When the engine is off, the Radiator Fan Control Module can control power to one or both fans. Fan switch B must be ON for the ground to complete its path. I can't tell from the diagram if one or both fan relays is getting power when the car is off. So I am not sure if one or both fans is supposed to run when the car is off.