Overheating due to ECU signal to cooling fan problem?
 

I have a '99 Volvo C70 2.4L Turbo Convertible and recently the cooling fanstopped coming on. Initially, I thought the problem was "faulty" reading by the coolant temperature sensor (that is located in the thermostat housing), since the dashboard temperature gauge is not showing that the car is overheating when it clearly is!! The funny thing is that the dashboard temperature gauge is at the bottom when the engine is cold and climbs steadily up to normal operating temperature (seems all normal) but will not climb higher when clearly thecar overheats (boiling antifreeze cracked the expansion tank)!! I flushed the system (hoses, radiator, engine), replaced the expansion tank,thermostat, and the coolant temperature sensor, andfilled it with new Volvo coolant 50/50. The cooling system does not have any leaks and is pressurized. The car is driving better thanever, howeverwith the new sensor installed the fan is still not coming on and the dashboard temperature gaugestill does not exceed the normal operating temperature while thecoolant gets way too hot!! I checked the fan motor by bypassing it to the battery and the fan-motor is fine. Then, I checked the relay (since this is the number one cause of fan trouble according to the Volvo dealership) bygrounding it and the fan comes on! The ECU does not present any problems on the dashboard, but I was thinking that maybe the fault is located in there or the connection from the ECU to the relay. Can anybody shed some light on my problem? Any information that you have will be so helpful!!! Thanks!!!

RE: Overheating due to ECU signal to cooling fan problem?
 

That is possible.
Does the fan come on with the A/C on?

RE: Overheating due to ECU signal to cooling fan problem?
 

Thank youso muchfor replying to my desperate cry for help!!The cooling fan does come on when I run the air conditioner!! https://volvoforums.com/micons/m9.gifWhat could be the problem? At what temperature of the coolant should the fan come on, and whydoesn't the dashboard temperature gauge exceed the "middle" (normal operating temperature) when the car is overheating?Thanks again for your help.

RE: Overheating due to ECU signal to cooling fan problem?
 

There must be an electrical problem with that circuit only.
I believe depending to the temp thermostat it should come on close to 200.

[quote=Sebastiaan;92136]I have a '99 Volvo C70 2.4L Turbo Convertible and recently the cooling fanstopped coming on. Initially, I thought the problem was "faulty" reading by the coolant temperature sensor (that is located in the thermostat housing), since the dashboard temperature gauge is not showing that the car is overheating when it clearly is!! The funny thing is that the dashboard temperature gauge is at the bottom when the engine is cold and climbs steadily up to normal operating temperature (seems all normal) but will not climb higher when clearly thecar overheats (boiling antifreeze cracked the expansion tank)!![quote]

Sebastiaan,

I assume you got this taken care of by now. I have the same problem. What was the diagnosis? Please.

i have exactly the same problem, does anyone know the problem to this? please i'm desperate, have done the whole engine over and now my heat gauge shows normal but my water boils and my fan does'nt kick in.

I have the same problem too, how did you fix it?

I had a similar prob with my 96 850
 

I changed the cooling fan relay. It is found on top of the radiator an easy repllacement.

same problem in my 01 s60