Corolla :: Cooling Fan Comes On As Soon As Ignition Is On

Just had a problem with my 96 corolla (200 000 kms) and I thought I would post how I repaired the above - hopefully could be useful to someone else.

Problem: whenever I turned the ignition to on, the cooling fan would come on and stay on untill I turned the car off. The car was behaving this way regardless of whether it was cold start or hot start.

In my case, the problem was the cooling fan switch (or some say sensor). It should test for continuity when engine cold. When the engine is hot, it should have no continuity. In my case, I had no continuity with the engine cold... so therefore the sensor 'tricked' the fan relay into thinking that the engine was too hot, hence the fan was always on.

Note that on this Corolla, there are two sensors (at least) for the cooling temperature. There's the cooling fan switch sensor and there's the sensor the sends the temperature to your temp gauge. That had me scratch my head a bit.... cause at first, I connected the car to an OBD2 and could see it was reading the temperature ok.... so I had initially ruled out the sensor... but a bit more research and I realized the fan has its own sensor.

How to fix it: The sensor is right underneath the distributor. Here's what I did:

1) empty about 2 litres of rad coolant into a clean container (you don't want coolant to leak when you take the sensor out.)
2) Unplug the sensor.
3) Pull the coolant overflow container out of the way. it's a slide in... just pull it up and out of the way.
4) Use a 17mm deep socket, remove the old sensor, pop the new one right in.
5) Reconnect sensor, put overflow container back on. Pour coolant liquid back in. make sure rad cap is on.
6) You're set. 30 minutes max.

Here's a picture of what the cooling fan switch looks like....