View Full Version : Coolant sensor unplugged --Coolant fan runs!

08-27-2013, 01:50 AM
I have a 1992 Celica GTS. I noticed the temperature gauge has been on the cold side. So I replaced thermostat and gasket. Still on the cold side. I unplugged the coolant sensor with the switch on and the fan run constant. Does this mean the coolant temperature sensor is bad. The service manual say you have to ground the connector to get the fan to come on. all I do is unplug the connector from the sensor. Any ideas?

08-27-2013, 01:55 AM
This is how Chaos runs, when we put her new engine in, we didn't have the upper coolant sensor, we left it unplugged. I throw a code (but no CEL) and the fan runs constant with the switch.

Other issues not withstanding, Chaos ran like this for two years.

08-27-2013, 01:59 AM
Murgatroy, I am going to unplug it and run it like that and see what happens. Will let you know.

08-27-2013, 02:02 AM
Keep an eye on the gauge, granted, this isn't ideal, but it isn't a death knell either.

Odds are good this is a safety feature, if the sensor fails, the fan runs constantly to keep you from overheating.

It is far from the first time I have run a fan from the switch.

08-27-2013, 02:27 AM
I just ran the car with the connector unplugged. No change in gauge. Still reading on the cold side. the weird thing is I have been running without the fan for awhile and the car has not overheated. At least to the point where the gauge showed hot.

08-27-2013, 04:40 AM
Which sensor are you talking about?

The sensor on the radiator is actually the fan switch temperature sensor, and is responsible for turning the fan OFF when the radiator's coolant is below 93C. Toyota designed it as a safety feature, so that if the sensor malfunctioned the fan would run constantly, as overheating is more dangerous to the engine than a lower-than-ideal temperature. Unplugging the sensor has the same effect.

08-27-2013, 08:43 PM
Yeah I unplug the sensor to test the fans, it's a lot easier than risking overheating to do it.