My S90 (200K miles) has been overheating in traffic. The electric fan never comes on. It used to behave as expected: fan on low if AC on; fan on high if car was hot when turned off.

The relay checks out OK--fan runs low speed if the contact that the Green/Orange wire connects to is grounded, and at high speed if the contact that the Yellow/Brown wire connects to is grounded. But with the car running, the Green/Orange wire shows no (greater than 30Megohms) connection to ground when the ac compressor is running. My wife tells me that the fan wasn't running after the upper radiator hose blew off while she was idling at the curb last week. Actually, the hose stayed connected to about a half-inch of the snapped-off plastic pipe on the radiator.

Questions:

1. What is the best way to test the temperature sensor? There's no connector--the sensor has two black wires spliced into two wires coming out of a spiral cable wrap that emerges from under the intake manifold. Those wires are Green/Gray and Gray/White, which agrees with my wiring diagram. I guess I'll have to cut the wires, then reconnect them after the test.

2. If it's OK, does it go back dry, or do I use a thread sealant, anti-seize, or a special Volvo washer?

3. As I understand it, the Temp sensor, good or bad, shouldn't affect the fan coming on if the AC is on, so is the problem really in
the ECU (or is it ECM)? Where is the ECU--under the dash?

Any suggestions would be appreciated.

Fred Brosi