940 e-fan troubleshooting

Yes, I know there are a million e-fan threads. I have looked at many of them and still cant understand it, mostly because there are so many different setups and scenarios.

I have a 1992 940 Turbo. LH 2.4

I replaced the Engine Coolant Temp (ECT) Sensor that is under intake port #3. I don't really know how to use a multimeter very well, but I think I figured it out, and the resistance that I was reading from the old ECT sensor was intermittent due to corrosion on the sensor.

There is no temp sensor on the radiator end tank as this is a turbo.

I ran the car for 10 minutes in 75 degree direct sunlight. The upper rad hose got pretty hot and the coolant level raised in the bottle. The e-fan still did not come on, even though the head was pretty hot.

I tried various A/C settings, but the AC doesnt work right now anyways.

the e-fan never came on without doing the following;

I shorted the grey (low speed) and brown (high speed) plugs that were on the AC condenser, and the e-fan itself does work.

My next thought is that it is the cooling fan relay, but I don't know how to go about testing that safely and without damaging it.

Would appreciate any help on how to test the relay (behind the headlight) or suggestions on other possible causes.

Thank you!

ECU grounds one of 2 wires depending on desired speed. Do you have the electrical schematic? I don't recommend touching anything without it. Or at least unplug your ECU for safety.

I do not have the electrical schematic.

I do have the link to this page

http://www.volvotips.com/index.php/...vice-repair-manual/volvo-960-wiring-diagrams/

but the image is too garbled to read, not sure if it's just me.

Do you mean unplug the ECU while testing the relay with the car running? Or can I just disconnect the battery while working on it?

https://www.myvolvolibrary.info/Tech_files2_ficheiros/940MY95_EN_Wiring_Diagrams_section-3-39.pdf

Go to page 50. I believe 95' fan diagram is same as your '92. As long as this is the case your fan relay always gets battery power and is grounded by either ECU or pressure switches for the A/C.

To check the relays you need to feed ground to BL/SB wire or W/SB. Do you have the same colors on your '92? Wire color abbreviations are on Page 2 BTW. The easy and safe way is to unplug pressure switches on the condenser and jump them- that should activate either fast or slow fan operation.

Car doesn't have to be running. Since there is a possibility that you can do something wrong (like backfeeding wrong polarity into ECU I recommend that you unplug the ECU just to be safe.

I really appreciate the link and your help!
Looking at the diagram on page 50:

(7/38) and (7/40) are the pressure switches on the condenser.

(4/23) should be the ECU, what is (C154) that it passes through, is that the ECT Sensor?

(2/11) appears to be the Cooling Fan Relay that is behind the headlight. This relay has 3 plugs, does that mean that that there is 1 plug for hi speed (from ECU/condenser), 1 plug for low speed (from ECU/condenser), and 1 plug from the battery?

I already jumped the plugs from the condenser before, and it got the e-fan running. Looking at this diagram, it seems that would indicate that the relay does work.

If that is true and it does indicate the relay is working, my thoughts are that it is (C154), (but I just replaced the ECT sensor?). Or, some sort of break in the wiring that runs from the ECT sensor to the ECU.

Do the ECUs ever go bad in a way like this?

From what you have tested- the fan relay is fine.

The driver for the relay can go bad inside ECU. But both (low and high) at the same time is less common. Not all ECU's have e-fan controls in them- are you sure yours is correct and it worked before? Wire connections can rust. Is your car overheating? How high does the gauge go? It usually takes forever for cooling fan on turbo 940 to come on at idle.

Does anything happen if you disconnect Temp Sensor while the car is running? I imagine Check Engine/Fault Code and it would trigger safe mode and ECU would turn the fan on to protect the engine. At least that's the strategy I've seen on most other cars.

I bought the car in the fall and it has not been driven much, only to the car wash and back, in cool weather. Can't say I've ever heard the e-fan come on.

I pulled the ECT sensor plug while the car was running. It struggled for a half second before catching itself. The CEL turned on and the e-fan kicked on. It stayed on with the key out, until I turned the key back to run. I plugged the sensor back in and restarted the car. The CEL was still on, so I shut down, disconnected the battery for a minute and then restarted, which cleared the CEL.

Maybe I just haven't let it get hot enough to trigger the ECU's temp level, but I don't want to cause damage by letting it overheat in my driveway. The Water Pump seems to work fine, what is the worst case scenario if I leave it idling with a non-working e-fan? Just in an effort to test it, that is.

If you try to let the temp gauge about 3/4 high before the red I don't think you are risking anything. Your fan will likely turn on before then.
Since the ECU turned the fan on as soon as it lost the Temp input I believe everything is working fine.

So I had to leave it running for almost 20 minutes, but the e-fan came on! Albeit only for about 5 seconds. However at least I have confirmation that it switches on from the temperature.

Thank you very much for your help and patience!

Just shows how efficient the cooling system is on them. Enjoy!

As I think was mentioned early in this thread, the head mounted sensor which inputs temp to the ECU must have a flawless electrical connection. There are cheap aftermarket sensors (KAE ?) which folks use..... I recommend the OEM BOSCH sending unit. Be certain to test/change the correct one! There is a simple temp. sensor in the head (can't recall which intake runner, near #3 and #4) that drives only the gauge (which is biased and doesn't report true temp).

My son made the mistake of putting a early LH2.4 ECU in his 92 9 sedan, which didn't have the driver for the E-fan! That experiment didn't last long. Confirm the ECU number for your 92. I don't recall this morning if the JETRONIC (fuel) or the EZK drive the fan output.... which of course is nothing more than a ground signal to actuate the relay.

Last thing - don't assume your radiator has good flow. Since these cars are approaching 30 years old, if your vehicle hasn't had a new radiator installed you should consider if it might be degraded/blocked. I like to gravity test the radiator by filling it from a hose and seeing if the flow is near equal. As PCH said, the cooling ability of these aluminum radiators is a huge improvement over the old school metal end tank radiators..... there is no comparison.

G-Tech 940 said:

So I had to leave it running for almost 20 minutes, but the e-fan came on! Albeit only for about 5 seconds. However at least I have confirmation that it switches on from the temperature.

Thank you very much for your help and patience!

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Yup, Volvo was kind enough to give us an oversized cooking system, but they *also* don't turn on the cooling fan until the coolant is pretty warm. I think roughly 225F for LH2.4 cars. They probably assume people won't often idle that long without the AC on (which should run the fan)

By the way, did you say your fan did or did not come on with the AC on, assuming the AC works well? It should come on in less than 30 seconds at idle most of the time, since AC pressures shoot up quickly at idle with no airflow.

DET17 said:

There are cheap aftermarket sensors (KAE ?) which folks use..... I recommend the OEM BOSCH sending unit. Be certain to test/change the correct one! There is a simple temp. sensor in the head (can't recall which intake runner, near #3 and #4) that drives only the gauge (which is biased and doesn't report true temp).

Click to expand...

Thanks! I did make sure to get a Bosch replacement. I would much rather buy the proper part than a ****ty aftermarket piece to save a few bucks.

I've got pretty skinny arms and flexible bones (just kidding) but I had to take the intake manifold off to change the ECT sensor. The sensor that drives the gauge is under inlet port #2, the ECT for the ECU is under port #3.

I think I probably could have awkwardly changed the sensor with only removing the throttle body, but I was following a RobertDIY video and he lost about a pint of coolant, I didn't want to be fumbling trying to get the sensor lined up while fluid gushed onto the floor, so I removed the inlet manifold. Turns out I only lost about a thimble full. I did the upper-rad-hose-squeeze-trick to get a bit of suction in the system, which seemed to work.

I had a set of phenolic spacers to install on the intake manifold, but I decided against it for now, as I might try to paint the manifold later on (in the winter) and don't want to have to clean gasket maker off of 4 surfaces when I do, so I just put a Reinz gasket on for now. I already replaced the studs with the longer Yoshifab ones for the spacers, but just left them in until I make the swap. (My next big job is replacing all of the exhaust studs, this was good practice although swapping the exhaust studs is still kind of daunting, I'm really nervous about snapping a stud off)

iHateVolvoPeople said:

By the way, did you say your fan did or did not come on with the AC on, assuming the AC works well? It should come on in less than 30 seconds at idle most of the time, since AC pressures shoot up quickly at idle with no airflow.

Click to expand...

My AC system doesn't work right now, I need to replace the compressor (was going to get a Nissen's unit) and one of the hoses , as well as the receiver/dryer. The clutch on the compressor does not engage unless the pressure switch plug (on the dryer) is jumped. The compressor leaks like crazy anyways so I imagine it needs replacing regardless. I also don't think it's had the R134a conversion as there neither the round nor rectangular light blue sticker is installed.

I tried playing with the AC controls just in case it would click the e-fan on (I'm kinda flying by the seat of my pants here, and learning as I go) but nothing happened.

Yeah the fan won't kick on until the pressure switch is activated (as you did) in the condenser. So with inoperable AC it will not kick on. It differs from a lot of other things like toyotas and Honda's that usually kick the fan(s) on as soon as the compressor is engaged.

BTW turbos use thermostat with lower opening temp. So coolant starts flowing through the radiator sooner than on n/a cars.