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940 cooling fan problem

Mr. V

Mr. V

Well-known member
Joined
Jul 5, 2004
Location
Portland, Oregon metro
1992 940 Turbo sedan.

I removed the AC compressor and did a lot of engine work: ignition, fuel: most everything was touched.

Now the electric cooling fan comes on when I start the car and stays running awhile after I turn it off, even when the engine hasn't had time to warm up.

Suggestions?
 
No belt driven fan: electric only.

I was looking for the sensor that controls the operation of the fan but cannot locate it with certainty.

This seems a newbie question, but I have to ask: Which sensor controls the fan, and where is it located?

I am looking at a schematic from a Mitchell manual and it is confusing.

Thanks.
 
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The sensor seems fine: it's new, and the temp gauge works OK.

Fan comes on and stays on.

I removed the AC Compressor: could it being gone / the power lead unconnected be causing the problem?

Bad coolant fan relay, perhaps?
 
Kjets On a Plane said:
You know the ECU temp sensor and gauge temp sender are different, right? One controls the fan relay via the ECU, one doesn't.
Click to expand...

Well now we're getting somewhere.

Yeah, I know there are three sensors that thread into the driver's side of the red block; I replaced the rear-most one, the one between cylinders 3 and 4, as a poster above said that was the one to replace.

I see that in front of that is a knock sensor (replaced) and in front of that, under/near cylinder number two is another coolant sensor.

Are you saying the sensor I need to replace is the front-most one, not the rear-most one?

Might the cooling fan relay somehow be involved?

Thanks.
 
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Further to KJ's point, there a pair of ground inputs to the E-fan relay. If you've "buggered up" the harness of the relay, you may be grounding 100% of the time. Find the small gauge pair of wires that enter the center of the relay.... one ground path enables HIGH, the other LOW. Logic behind "WHY", below.

All the details, and truth you seek, can be found in the Volvo UK 700/900 Maint. pages. There are experts here... and lots of rank amateurs! Follow the seasoned advice in those pages, and your machine will be happy.
 
That’s an aux fan relay, same as RSR. The main cooling fan on your car is more like 2 or 3 relays built into 1 unit. And it’s a lot bigger.
 
Mr. V said:
I just discovered my car had the relay described below, clipped onto the driver's side fender tucked behind a wiring harness near the ignition amplifier / module:

https://www.ipdusa.com/products/10669/124103-relay

Could this be a possible culprit?

I didn't know the car had it; seems sort of like the radio suppression relay on a 740, but I'm not sure what it controls.
Click to expand...

That is your radio suppression relay. It drives the injectors. No, the front temp sensor has nothing to do with the e-fan. It is the sensor for the temperature gage in your instrument cluster, nothing more. The sensor I described above is where the ECU gets its temperature readings for all its functions, including turning the e-fan on and off. Either it is not sending correct readings to the ECU, the ECU is defective, or, you have a short in one of the wire that triggers the fan relay. It could even be a bad fan relay itself.
 
Where is the ECU on this car, is it behind the kick panel by the passenger's feet as with a 740, or someplace else?

I will troubleshoot it before going to a shop.
 
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Follow up:

The problem was a faulty coolant sensor, the one between cyl 3-4.

What threw me for a loop is the fact that while working to correct the problem I bought and properly installed a new sensor from IPD and assumed it was working: it wasn't, it was defective.

From now on it'll be OEM sensors, not aftermarket.
 
Mr. V said:
Follow up:

The problem was a faulty coolant sensor, the one between cyl 3-4.

What threw me for a loop is the fact that while working to correct the problem I bought and properly installed a new sensor from IPD and assumed it was working: it wasn't, it was defective.

From now on it'll be OEM sensors, not aftermarket.
Click to expand...

You are not the only one on here that has encountered that. I won't install anything other that a Bosch sensor for that particular sensor. Even then, I take ohmmeter readings cold and warmed up after installing the sensor. That sensor is the most important sensor in your fuel injection system.
 
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