So today I noticed a wire disconnected from my cooling fan relay. I reconnected it, and the fan went on. The car was cold, and hadn't yet run today. I had planned a trip to the junkyard today anyway, so I picked up a new relay. Put the new relay in and the same thing happened.

I was looking for wiring diagrams, and I'm not sure where to look. I have access to the VADIS software, but couldn't find diagrams in there.

John

 

This may help.


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[IMG]local://upfiles/14053/F727F7C55A134CE2BF6B3935F4E33DDC.jpg[/IMG]

 

A bad ECT sensor will cause your problem. How is your temp gauge reading?

...Lee

 

The diagram isn't too helpful because nothing is labled as what it is.

It seems the computer is telling the fan to go on, but what are the inputs to the computer that would cause this?

My temp gauge is fine. Reads 1/2 up at the most, most of the time runs about 1/3 of the way up.

For now I've wired a switch in the dash in series to the wire that is turning it on (pin one of the middle connector as I recall) so I can turn the fan off and on from inside the car.

What is a ECT sensor?

 

+1 on the ECT. ECT = Engine Coolant Temperature sensor. My cooling fan stayed on all the time when mine went bad. OF course the car ran rough until it warmed up and I had a check engine light too. Is your light on, Any codes.

The sensor was about $15 and is located under the thermostat housing

 

I would assume that sensor would also cause the temp gauge in the car to read incorrectly. Mine reads normally. Also the car runs OK cold or hot. It does have an intermittant P1033 code when hot, but I'm sure this is unrelated.

I saw a post about another sensor under the intake manifold, could this be causing my issue?

 

IMO, if your temp gauge marks 1/3 temp then either the ECT has a problem or your thermostat is stuck open.

The temp gauge should be at half or a tiny bit higher.

Another guess during this time of the year would be that you live in Antartica.

 

Well maybe it sits closer to the 1/2 mark on days like today. I dont' drive it far, and when it is nice out, I usually drive my convertible.

So maybe my thermostat is opening early, but that wouldn't be causing the issue I'm trying to solve. Probably worth replacing at some point, but stuck closed is a much more serious issue

John

 

Antartica [sm=smiley36.gif].

ECT = Engine Coolant Temperature sensor.


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Have you tried swapping cooling fan relays with another car?

 

Yes, see my first post. I put in a different relay and had the same results. Looking for what, other than the temp sender on the thermostat would tell the CPU to turn on my fan. Now I suppose it could be a bad CPU. There are two CPUs in the container on the right side of the engine compartment. Which one controls this? I could pick another one up at the junkyard for $25.

John

 

Hello Quincy56,

This one may be of more help to you [sm=smiley20.gif].
http://www.volvoclub.org.uk/tech/ser...CoolingFan.pdf

I may just be able to read the firstschematic a little better.


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I had that one from the VADIS software. It looks like the only other input to the computer is the high pressure switch on the AC. I've disconnected that and it doesn't seem to make a difference.

 

Sorry, I wasn't paying attention.

There are two control signals going from the ECU to the fan relay: high speed and low speed.

I understand that the ECU activates the high speed signal when the ECT sensor says that the engine is getting too hot, and low speed to help air flow through the condenser to control pressure on the high pressure A/C side. Don't quote me on this, it´s been about 3 months since the last time I tried to troubleshoot my fan before giving up.

I wonder what the ECU does when the ECT signal does not make sense or the high pressure switch is bad. I'd love to look at the source code for the Motronic software

The Motronic module controls the signals sent to the fan relay. IIRC mine says version 4.3 on a white sticker.

 

The temp gauge should go to the 3:00 position within a mile or so of driving and be nailed there (It may be a needle width high or a needle width low from that depending on where the gauges were after the odometer gear repair). If it floats around like you describe the the thermostat and/or the ECT sensor is bad. It is customary to change both of them at the same time. Get the new style bolts before you even start. If you have the original bolts chances are you will strip the head on one or both trying to get them out.

...Lee

 

Both of the sensors? I know of the one at the thermostat housing, where is the other?

 

When he said "both", he was referring to the thermostat and the ECT. There is only one sensor, it's inside the thermostat housing.