The car: 97 Legacy Outback Wagon 5spd 179K miles, No check engine codes showing

 

The problem: (1) Fan runs constantly. Temp reads normal, heater works fine,

(2) High idle when cold, up to 2500rpm, meaning I really have to warm the car up before taking off or shifting becomes a clutch-eating chore.

 

So I read numerous threads here that seemed to point to the CTS, coolant temperature sensor, as the culprit, possibly for both problems. Today I bought an OEM sensor and replaced the old one. I did the PCV valve while I was in there. Fired up the car when I was done and it reved way up and the fans ran just as was happening before!

 

So what should I check next? The temp gauge sender? I thought of replacing it too, but the gauge reads normal so I thought it was surely the coolant temp sensor.

Some threads referred to vacuum leaks as a cause for high idle. I think it's possible I have some leaks somewhere because those hoses near the sensor I replaced are pretty brittle, but that doesn't explain the fan running.

Maybe I have two separate problems? Any ideas?

Thanks!

Did you replace the two wire sender or the one wire sender?

Both senders are thermal resistors. Their resistance changes based on how hot they are.

 

The ECU gets it reading from the two sire sender. It feeds the sender 5v through one wire, and reads the drop in voltage through the second wire.

 

The one wire sender is for the gauge. It just grounds a 12v feed through the gauge, the gauge reacts to the voltage change due to the resistance in the sender.

I replaced the two wire sensor. Maybe the one-wire sender unit is the problem?

The one wire sender is only connected to the temp gauge and not to the ECU. It cannot be the cause of your problems.

The one wire sender is only connected to the temp gauge and not to the ECU. It cannot be the cause of your problems.

What he said.

 

Did you check the voltage at the sensor to make sure it is getting 5v?

This happened to me on my 96' Legacy not to long ago..not to mention I've seen it multiple times on customers cars.....My bet is that your thermostat is stuck..sometimes this will throw the cooling fan rationality check code however on my car it did not...I personally would start off by making sure the system is full of coolant, than make sure there are no air pockets..if both of those check out I would be inclined to think the thermostat is stuck...especially if you have never done one on the car and you have owned the car for a good while...Also has the cooling system had any other recent maintenance besides your replacement of the CTS?...

Say, has anyone plugged in the green diagnostic connectors to each other under the dash? That can make the fans run on.

As I recall , the fans will come on when the AC is on, or pressure is sensed in the AC coolant line switch.

 

Not near my subie right now, so I can't tell you where to find it, but try pulling any fuse for the AC system, then start the car/

-Do you have access to a scan tool? I would suggest reading out what it says the coolant temperature is... that will verify the wiring to the coolant temp sensor.

 

-Remember, the A/C is on when you're in Defrost mode, so the fans will run.

 

-I don't think 2500 rpm is unusually high for a cold start, but it should begin settling down very quickly if all is well.

I'll see about borrowing a scan gauge to check coolant temp. I have replaced the thermostat within the last 30k miles, and the car warms up normally and runs at normal temperature according to the temp gauge, so I really doubt it's sticking. The radiator and water pump were replaced about 40k miles ago when the head gaskets were replaced. The cooling system seems to work as it should, but the fan won't stop.

This morning I played around with relays, switching in ones that I knew were good. It made no difference, the fan still runs as soon as the key is turned on. I am at a loss.

Stuck relay? Making the fan stay on? Just throwing that one out there? I've had relays get stuck in the opposite way where the fan wouldn't come on.

Say, has anyone plugged in the green diagnostic connectors to each other under the dash? That can make the fans run on.

 

Yeah, but it would just cycle on and off every 2 seconds or so, not stay on constantly. And all the lights in the dash, and all the relays and solenoids on the car would be flipping out too. Least that's what mine does in test mode.

 

I have heard of similar problems to this with some older GM cars (early to mid 90's) . It usually gets fixed by installing a new ECU.

 

Does the check engine light come on when you start the car?

No the diagnostic connectors are not plugged together. The check engine light is not coming on either. I thought for sure it would be the coolant temp sensor. What else would control the fans coming on and off?

The coolant level may indeed be low. I thought it was fine last time I looked, but I'll check it out when I'm near the garage again.

Thanks

The CEL should come on for a few seconds when you start the car and then go out. If it doesn't come on at all the bulb is probably burned out.