1998 S90 Electric cooling fan runs long after engine off.

[Pilgrim999]

The electric cooling fan runs on for 5 minutes or so after the ignition is turned off, resulting in draining battery. Replaced ECT sensor (under thermostat) and thermostat; problem disappeared but started up again in about a week.
This morning I started the car, then shut it off after a few seconds; the fan kept running, even though the coolant was dead cold. I disconnected the fan relay (next to the battery); the fan stopped, but resumed running when I plugged the relay in again right away. So, I unplugged the relay again; when I did that, I could hear a faint humming from the right side of the engine compartment (in the vicinity of the alternator); after about 5 minutes there was a faint click and the humming stopped. At that point, I could plug the fan relay back in without it starting back up.
Is there another relay for that fan, maybe one with a timer on it? And the more general question is: how can I stop the fan from running on and depleting the battery?

[93Regina]

Replaced ECT sensor (under thermostat) and thermostat; problem disappeared but started up again in about a week.

I know nothing, but from looking at schematic, there is some-type of "logic" device (maybe ECM) that appears to control both low/high fan-speeds.

From another forumn, in post #9, the second schematic shown is fairly typical.

The ECT and the AC High Pressure Sensor sends the signal to ECM.

It would take a logic probe & voltmeter to figure out which device is sending the trip-signal

Pin 25 (ECM) appears to be a trip signal, but there are pins 29/28/9 which appear to go to the AC pressure sensor, but I can't tell which wire is the trip signal.

Hence, try unplugging your AC high pressure sensor, and see what happens.

Has the front end of your vehicle been modified...so air flow would be affected?

Warning - When AC high pressure sensor is unplugged, do not run AC