Yaris 2005 coolant sensor

May 6, 2022

Hi all ,

my mrs as a 2005 mk1 yaris and the other day the electric fan came on . She was only driving local and the weather was not to hot and neither was she stuck in traffic .

I have checked coolant level and they seem ok .She did get a engine light on saying coolant temp bank 1 or something very similar .I was thinking of changing the thermostat ,would this help ? Also where on the car is the coolant sensor ?

many thanks

May 7, 2022

I had exactly this happen a couple of years ago and like yourself I came close to replacing the thermostat and coolant sensor. It did, for myself, though, turn out to be a much simpler resolution.

Fortunately at the time I had access to another Yaris. What I did was swap the engine-fan relay from one car to the other. This is the orange relay housed in the fusebox under the bonnet. It will require a bit of a tug to withdraw. Upon substituting the relay from the other vehicle and starting the engine it was immediately apparent that the fan was off – it had previously been on continually. So I took this to mean that the removed relay was at fault and the other car’s fan would now come on. It did not and I found this quite confusing. So I transferred both relays back to their original positions and guess what? Neither fan came on. I am unable to explain why this should happen as once the relay is seen to fail - somehow setting itself and closing the engine-fan circuit to run continually – I cannot see how this condition would change just by removal from the fusebox. But change it did and the problem ceased forthwith.

So please give this a try – just remove the relay for a couple of minutes, then return and then startup. Fingers crossed. 🙂