I have a '96 Legacy with a 2.2L. Runs great, but idles a bit low. It recently had the check engine code come on, scanned it and P0115 (coolant temp sensor). It came on when the weather was very cold (around -10F for a week), and as soon as it warmed up outside a bit (25-35F), the check engine light went out again. Now that it has cooled outside again (around 0F) the check engine light has come back on.

 

Replacement looks simple enough http://www.lovehorsepower.com/SubaruDocs/CoolantTempSensor.html

 

but I am just wondering if it is really the problem. It does make some sense that it is having issues when the temperature really drops, but wouldn't it be having issues the rest of the time?

 

Also, anyone have experience with aftermarket replacement sensors? any good?

I have had this code get thrown before from low coolant level..first I would go out and check and make sure your overflow and radiator are both full...Replacement of the sensor isnt too bad just a tad of an awkward position to get your hand down there and get the threads started...If you do end up replacing it make sure the little washer is on the sensor before install...Ive seen people forget these and some of them leak a tad.....

I have replaced two on two different cars.

The firs time (a Loyale) the CEL was on for a long time (weeks) before the car had any serious symptoms (no start when hot and stallings).

The last time I had the symptoms before the CEL came on.

I would take the CEL seriously (check the connection to the sensor first though) and replace it. It's not very complicated but it's a little involved. Ill placement and lots of tubes and wires in the way.

Finally, I dont remember the OEM sensor to be very pricey. I would use a Subaru one and not skimp on anything having a direct connection with the ECU.

My two...

G.

I'm a strong believer in having a good (read, new!) ECTS. The ECU needs the best info it can get to manage the engine properly and accurate temp. readings are crucial.

 

However, it could be that your CEL was just a fluke because of the extreme outside temps.

 

I'd suggest you keep driving it as is--it probably won't leave you stranded. Just be aware of any changes in engine operation, especially if it has a hard time starting when the engine is warm.

 

And if/when you replace it, I'd use Subaru OEM part.

 

Good luck.

+1 on low coolant causing this code...replaced one once after doing head gaskets and didn't re-check the coolant level...was just some air in the system.