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1996 Subaru Legacy, 2.2, manual, 133k
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Discussion Starter #1
Hi, I have a 98 legacy with the 2.2, 241k, runs real well but Iv been noticing once the engine warms up the cooling fan (driver side one) starts and never shuts off till the engine is turned off? Engine is not running hot, gauge is in the middle and I can lay my hand on the valve cover after a half hour highway drive. Coolant is newish, full and I'm not loosing any. Any ideas?

Chad
 

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Make sure the heater vent outlet control is NOT set to either of the two windshield defrost positions and that the heater fan control is set to OFF.

If that doesn't correct it, then it could be a faulty engine coolant temperature sensor. That engine has two coolant temperature measuring devices -- the engine coolant temperature sensor, and the coolant temperature gauge. The first one supplies temperature information to the engine control module, which in turn controls the radiator fans. The second works with the instrument panel temperature gauge. Although rare, it's possible that the sensor is causing the ECM to turn on the fan while the temperature gauge on the instrument panel is still reading normal and in fact the coolant temperature is normal.
 

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2013 OB 3.6R Limited, Black Silica
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also, if the ac is on, whether auto or manual, in most cars that automatically kicks in a fan. We had a sloppy 0c day when i first got my OB a couple weeks ago and the full auto mode kicked in the ac to reduce humidity, which also started the fan, and it was 0c so not warm out. I was checking under the hood for the first time(while it was warm out) which is why I noticed the fan running.
 

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To add to Plain OM, the ECT sensor is the two wire sensor.

Both fans turn on with the AC and cycle on/off with the compressor.

The single fan running is most likely a sensor issue or a fused fan 1 relay.
 

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1996 Subaru Legacy, 2.2, manual, 133k
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Discussion Starter #5
Well i installed a new engine temp senor and switched in a different relay and it still does the same thing. :confused:
 

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. . . switched in a different relay . . .
Driver side fan is the "main" fan. According to the wiring diagram, the main fan motor has two speeds. The speed is determined by "main fan relay 1" or "main fan relay 2" being energized and sending power down one of the two wires.

I'm not sure where the "main fan relay 1" and " main fan relay 2" are located; I suspect they're two of the four relays in the main fuse panel in the engine compartment.

There's a third relay, which is located at the interior (cabin) fuse panel.

Which relay did you switch? Rather than switching relays, which could just move the problem from one relay position to the other, I'd tend to pull one of the relays to see what happens, and if nothing, replace the relay and pull the other. If the fan stops, then you know the source is in that particular control circuit. (But that doesn't mean there's a fault there -- it could be normal functioning; see below.)

What is strange, however, is that it appears the fan doesn't start running until the engine temperature is near normal. A short or jumper (both good ideas) would not seem to be dependent on engine temperature -- they would cause the fan to come on as soon as the key is turned to ON. In this regard, I understand that the fan stops when the engine is turned OFF; but that leads me to a question: When the driver side fan is running, and it seems unusual, what happens if the engine is turned off, and then key turned to ON? Does the fan come back on as soon as the key is at ON?

We can't discount the possibility that the coolant is, in fact, running on the hot side and the ECM is keeping the one fan on all the time once the engine is up to "normal" on the temperature gauge. The gauge has a flat spot" at that point -- it doesn't move much even though the coolant temperature can range from approx 85 C to 100C without the pointer changing noticeably, but the fan control would turn the main fan on at slow speed at approx 96 C.

Given the symptom, and assuming the relays are not the problem, perhaps the best way to verify what is happening is to see if there's a way, on the 98 2.2, to read the temperature that the ECM is seeing. This is possible on later years using some scanners and scanner programs. (cardoc -- any scanners that would work?)
 

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Any generic OBDII scanner that read data works. It is a possibility the gauge sensor is bad.

It could also be the relay is sticking after the first engagement. The fuses for the fan relays are controlled by the ignition switch and are dead with the ignition off, so power is cut, relay cools, opens back up.
 

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Thanks cardoc:

Indeed; temp gauge might be incorrectly indicating "normal" when engine coolant sensor is telling the ECM something else.

Or, as you note, a relay could stick once energized. Reading the engine coolant temperature might also identify if that's the case -- if the ECT is below approx 95C, the fan should shut off.

Back to chad_m . .
 

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1996 Subaru Legacy, 2.2, manual, 133k
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Discussion Starter #10
Thank you all for the great information! Engine runs fine, fan does not turn on till i get driving i guess, lately with the very cold temps here in PA the temp gauge goes back and forth from center to alittle lower then center, im guessing from the fan running. After an hour commute home i can open the hood and lay my hand on the top hose and its hot but not burning hot, radiators cooler yet, so i don't see the engine running to hot. If i shut off the engine and restart right away the fan stays off till i drive. Coolant, wp, hoses thermostat and cap only about a year old.
 

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So it appears that the fan remains off until the first engagement, remains on until the key is shut off. Upon restart, no fan until driven and the first engagement occurs.

A sticking relay is the most likely culprit. Which relay did you change the first go round? If it was #1, Change #2 and vis a vis.
 

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Hi, I have an even more complex issue. Anyone with ideas? 2003 Subaru Legacy. Start car all is fine. Sit in driveway cooling fans come on and shut off appropriately. Drive around neighborhood no highway everything seems fine. Drive more, get on the highway, engine temp fine without fans on, fans go on and do not shut off. Get home sit in driveway, fans will not go off. Shut off engine go back to ignition, fans still on. Let engine cool enough, i.e., cold fans off at ignition. Sensor seem OK in driveway, relays have been checked and replaced to double check and they work in driveway anyway. I AM STUMPED!!
Thanks
 

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Old thread.
So the fans may be on due to a stuck AC relay or AC pressure switch. If the ECM sees high pressure on the AC system it will turn on the fans. It will also turn the fans on if the ECT sensor is sending back high current or unplugged. When it does it and it's the ECT it's to insure the coolant is getting air flow to keep the engine temps down. When it does it due to the AC system it's thinks the AC pressure is high. If it's the AC relay, well, that's just a stuck relay and the system is turning the fans on because it believes the AC is on.
 

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Hi Cardoc, Thanks very much for your reply and the effort you put in. It seems like my situation is really not straight forward. As I explained before, if I start the car from cold in the driveway and let it idle all is fine. (the idle may be a little high) That is the fans will come on and go off repeatedly and they will not stay on long. Then I go out for a drive. As soon as the fans come on they will not go off and they will come on eventually even if the engine temperature does not close the thermostat sensor. Once on they will not shut off. You can sit at idle, they will not shut off. You can turn off the engine and see the temperature gauge indicate well below operating temperature and put the key to the run position and the fans will come back on. You can restart the engine and the fans will come on. They just will not go off. Then if you let the care sit for say 10 minutes and it really cools off the fans do not come on. It seems like something is getting stuck in the ECU once the car is driven. Any other thoughts. I am going to try and adjust the idle even though it has no effect on fan operation upon starting the car. Thanks
 

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@Blurscooter

Adding to post #15 above:

If only one fan runs continuously, then which one (driver or passenger side), and,

Is the engine the 4 cylinder or 6 cylinder?

@cardoc

If the ECM sees high pressure on the AC system it will turn on the fans.
Apparently the fan or fans continue to run when the engine is off. It has been my understanding that if the engine isn't running, the ECM doesn't take into account the status of the HVAC. In other words, if there's unduly high pressure in the AC system, I don't think that would lead to the fans being turned on. Similarly, if the HVAC blower fan switch is Off, it was my understanding that the ECM would not turn on the fans, unless, of course, the engine coolant temperature is high.
 

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Both fans run. On my 2000 Legacy the fan comes on in the defrost position and for AC like you mentioned. Otherwise it just comes on to cool the engine. This 2003 just putting on the internal blower can get the fans going. I can go under the hood and pull fuses and relays and make either fan work or no fans work. Somehow they are getting the wrong signal to turn on. Thanks
 

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In his post #12 he doesn't indicate whether the AC is on at the time or not. I was referring to a failed/failing pressure sensor that may be giving high pressure feedback. Don't know if he has Auto AC or Manual, so it was an idea thrown out.

Given what's in post 14, it seems that a relay is sticking closed after the engine bay heat, or electrical loads, heats it up.
 

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Both fans run. On my 2000 Legacy the fan comes on in the defrost position and for AC like you mentioned. Otherwise it just comes on to cool the engine. This 2003 just putting on the internal blower can get the fans going. I can go under the hood and pull fuses and relays and make either fan work or no fans work. Somehow they are getting the wrong signal to turn on. Thanks
All Subarus turn on the AC in defrost mode regardless of temperature setting.
Do you have auto or manual AC?
Is the AC button pushed and lit up? If it's manual.
Does the AC button light up at all? If it's manual.

The fan system is 2 independently controlled systems. See wiring diagram below. So if both fans are running that means the ECM is sending a ground to both relays. The only thing the fans share is the ground, but without power from the relays as commanded buy the ECM the fans won't get positive power.

That leaves a false signal to turn both fans on simultaneously.

Can you hook up to the car and see what the temperature reading through the ECM is? Any handheld scanner should see the ECT value. Since your temp sensor is 3 wire, one part sends feedback to the ECM, the other sends feedback to the gauge. The gauge portion may be correct and the ECM value is wrong. Or vise versa and your car is overheating.

Gen 2 USDM cooling fans:

496170
 

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This 2003 just putting on the internal blower can get the fans going.
cardoc is on the right track, but I'm puzzled by this report that turning on the internal cabin blower turns on the engine radiator fans. Is that with the engine running? If it is, then what happens when the engine is not running but the ignition switch is at the ON position? Does turning on the internal blower still cause the radiator fans to run?

As was noted, if the HVAC is set to AC, or if the mode is set to one of the two windshield defrost positions, and, if the engine is running, turning on the cabin blower can turn on the AC and that will turn on the radiator fans.

But, if the ignition is at ON but the engine is not running, the setting of the HVAC controls and blower switch should not have any effect on the engine radiator fans.
 
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