Hi, This is my first time posting..And my first Volvo.
Problem is the cooling fan wont run. I have tested the fan relay by jumping the control wires to ground (yellow and yellow /white). Then the fan switches on and off.
I have replaced the temp sensor and the gauge never goes above half way, but the engine gets so hot I can start to smell antifreeze. I jumper d in a variable resistor so I could trick the ECM to think it was hotter. The Gauge went up and the fan ran. It will run the next time I go for a drive, but not after that. I also noticed that the fuel gauge wont go above half way with a full tank of gas.
I think I have a bad ECM.
Is there a way to calibrate it?
Am I just overlooking something simple?
Any help is appreciated.

 

Hello, did you ever get to the bottom of this? For the last year I have had an earth wire running from the relay to my cigar lighter that I plug in every time I start the engine. The 850/V70 and the newer V70 temp gauge is only for decoration. I wrecked my 850 when the rad leaked and the engine got so hot oil leaked and head gasket failed - dash temp gauge stayed normal. I have a 2002 V70 where the fan won't start, the indication that it was hot was NO OIL PRESSURE STOP message and again temp gauge said no problems

 

It was very interesting that you were able to fool the ECM into turning on the fan relay.

Did you ever solve this problem?

I too am suffering from the same issue.