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No Fans or Coolant Temp.. Need Quick Help


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So as soon as I turn on ignition, my coolant temp shows way beyond hot on the gauge. Even when cold. It never fluctuates at all. Also, my radiator fans never turn on. Has anyone had an issue like this? My two guesses are bad temp sensor, or bad/no thermostat?
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The actual temp sensor (ECU) is the one located up higher towards the hood, the temp gauge sensor is the one lower down on the left.

 

If it pegs immediately to hot its bad if it does that overnight. I would ask to see if it were an air bubble or you had the system open for service recently but if it does it when its absolutely cold than that sensor is bad.

 

 

Fan control gets input to relay from the ECU. Easiest to first check fuse (13) - relay/wiring - and then finally the fan motor itself. You an jump +12V to either (low) or both (high) of the non black (ground) wires on the fan motor to make sure that it works.

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So as soon as I turn on ignition, my coolant temp shows way beyond hot on the gauge.

 

 

Have you done any work lately to the car?

 

 

I've seen this once, when I accidentally swapped the connectors for the coolant temp sensor and the evap system . There were three connectors in that area and when I was reconnecting them I noticed they all had the same type of connector so could be mixed up.

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Verified it's the right plug. It's brown and also the same connector on my spare motor. I unplugged it and the fans came on. I wish I could upload a picture of the gauge. The needle is basically at about a 2 on a clock when the max on the gauge would be around 11 on a clock..
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Do you have a way to check fault codes. If the coolant sensor is shorted out you should see a fault code for that.

 

 

If you're doing an engine swap maybe the engine wiring harness has a different pinout which could cause this issue for you. May need to compare wiring diagrams.

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No CEL with it plugged in, but fans don't come on. CEL comes on when i unplug it, but the fans come on. That's how I have it now just to cool it off extra since I don't know the temp. Could it be bad thermostat potentially?

No engine swap, just 5mt swap.

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Temp sensors. Replace both of them. One controls ECU input and the other one controls gauge output.

 

The one with a single wire is the gauge sensor. It works off of resistance. If the guage is pegging well beyond hot, it is detecting a spike in resistance to the gauge. Unplug the sensor and turn the car on. If the gauge is still pegged, there is a short in the line. If not, the sensor is defective.

 

To diagnose the cooling fans not kicking on, refer to the FSM Diagnostic Manual (linked below), pages 10-32 Cooling System Diagnostics. It takes you through every step of testing the fans and the harness.

 

http://jdmfsm.info/Auto/Japan/Subaru/Legacy_Outback/1999/Service%20Manual/DIAGNOSTICS%20SECTION.pdf

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