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Discussion Starter #1
Problem:
there are two fans
  • when A/C off, radiator fan does not turn on automatically
  • when A/C is turned on, both fans turn on and off at the same time automatically
  • engine temperature gauge shows overheating if I'm not driving up to speed.
Troubleshooting Steps Performed:

  • radiator coolant was flushed and refilled/ radiator cap was replaced with new OEM
  • replaced with new OEM thermostat
  • checked relay fuses to radiator and A/C fan
  • unplugged the coolant temperature sensor in engine bay. Check Engine light on dashboard comes on
  • replaced the coolant temperature sensor with new OEM.
  • hooked up the two connectors under the steering wheels and turn key to test the relays and fans - they all click and fans comes on both speed.
So what am I missing here? Still cannot get the fans to come on when the engine temperature rises.

Any info will be greatly appreciated

Thanks,
 

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Can you look at ECU info? What is the ECU seeing? Can you independently verify temperatures with an IR gun?
 

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I have the same issue, but it is intermittent and accompanied by an unstable idle speed(and occasional stalling). I used FreeSSM and ROMRaider to confirm a bad reading coming from the throttle position sensor. I put in a TPS and the reading was still out of spec. I eventually traced it down to a short somewhere in the wiring harness very close to the connector. So now, when the engine idle misbehaves, I "adjust" the wires with FreeSSM running till the TPS reading shows the throttle closed (ignition on, engine not running). At SOME point I'll trace down the two or more compromised wires and make the necessary repair. Till then, I just tweak the wires.

AFAIK, there are two wires from the temperature sender... one goes to the ecu & the other to the dash gauge.Im guessing the throttle position sensor wire is in the same bundle of wires.
 

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Discussion Starter #4
Can you look at ECU info? What is the ECU seeing? Can you independently verify temperatures with an IR gun?
i dont have anything to check the ECU, but I do have a IR gun to check the temp and its showing 220 degrees. Maybe I should get something to check the ECU. Should I just buy a Bluetooth one on amazon?

I have the same issue, but it is intermittent and accompanied by an unstable idle speed(and occasional stalling). I used FreeSSM and ROMRaider to confirm a bad reading coming from the throttle position sensor. I put in a TPS and the reading was still out of spec. I eventually traced it down to a short somewhere in the wiring harness very close to the connector. So now, when the engine idle misbehaves, I "adjust" the wires with FreeSSM running till the TPS reading shows the throttle closed (ignition on, engine not running). At SOME point I'll trace down the two or more compromised wires and make the necessary repair. Till then, I just tweak the wires.

AFAIK, there are two wires from the temperature sender... one goes to the ecu & the other to the dash gauge.Im guessing the throttle position sensor wire is in the same bundle of wires.
I've notice that the issue does seem to be intermittent now since its cooler. In the summer time with the A/C on, the temp just shoots up. I'll try to check the wires when I have free time.

thanks for the input guys
 

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Interested in hearing how this shakes out - I'm having similar behavior in my 2008 H6 but my temperature gauge on the dash has stayed locked at the 9 o'clock position (I drive with the AC on here in VA from basically April to October, so the fans are running).

When I connect my green clips and turn the key to 'On', my fans cycle through the speeds as well but I'm not very wiring-savvy so I'm not sure how much further I can go from here myself.
 

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On some Subarus, the ECT (Engine Coolant Temparture) sensor has TWO detectors within it.
*) ONE feeds the dashboard temp meter
*) TWO feeds the computer.

What this means is that it is possible for the gauge to read just fine...while the computer is being fed bad information. This usually results in a rich-running engine and may affect the fans if they are controled by the computer.

On other Subaru, the fans are controlled by a TOTALLY SEPARATE sensor unrelated to the two I mention above. In this case, only the fans would be affected.
 

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On some Subarus, the ECT (Engine Coolant Temparture) sensor has TWO detectors within it.
*) ONE feeds the dashboard temp meter
*) TWO feeds the computer.

What this means is that it is possible for the gauge to read just fine...while the computer is being fed bad information. This usually results in a rich-running engine and may affect the fans if they are controled by the computer.

On other Subaru, the fans are controlled by a TOTALLY SEPARATE sensor unrelated to the two I mention above. In this case, only the fans would be affected.
Interesting - how might I go about figuring out which category my car falls under?
 

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You have 5 fan relays. 2 for each fan motor in the AC relay holder and 1 that is in series with the ECM. The main motor is on the left side of the car; sub fan motor the right, (looking from the driver seat).

Each AC control relay set has it's own 30A fuse. There is also fuses FB1, 17 and 18 that supplies battery to the relays. FB 17 supplies power to the fan relay connected to the computer.

When you turn on the AC, the AC relays are energized to operate the fans. When the temperature comes up, the ECM turns the fans on via the fan relay. If FB17 is blown, the fan relay doesn't have power to it and the fans won't come one. If the relay is bad, it would work sporadically or not at all.

Gen 2 Fan diagram.gif
 

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@cardoc

In regard to the 2004 H6 . . .

hooked up the two connectors under the steering wheels and turn key to test the relays and fans - they all click and fans comes on both speed.
(bold added).

Here's a clip from the H4 Cooling section in the 2004 FSM (this same text is found in the corresponding Radiator Sub-Fan System page):

471118


From this it looks as if the fans run at three different speeds, depending on the ECT and AC load conditions. This is also suggested by the 2004 radiator fan wiring diagram attached earlier, which shows four connections to each motor. Therefore, when the green test mode connectors are attached for relay and solenoid testing, it seems to me the fans should cycle from off through three speeds, not two.

If that is correct, then perhaps the green connector test should be run again to check if the fans do run at three, or only two, speeds. If only two, that might provide some clue as to why the fans don't come on in response to coolant temperature only.

Also, if during the green connector test both fans run (regardless of speed), that confirms all the related fuses, i.e., the two 30 Amp fuses, SBF-1, and fuses 17 and 18.
 

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I don't think it's a fuse either. I believe it's a relay or a connection between a relay and the fans. Could even be a problem with the winding in the fan(s) themselves.

Also, I had a fan issue some years back that ended up being the alternator as the source of the issue. So check your conductance between the ALT fuse and the alternator. Check it also from the alternator to the battery, then check the alternator output idling and driving, (if you have a scan tool that lets you see alt current while driving).
 
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