iQ Overheating Issue

I had almost the same thing with my 2012 Opel Corsa: overheating and the check engine light. For me, it was a bad thermal switch that wasn't regulating the temperature, so the fan wouldn't turn on. Before you replace the speed sensor, check the thermal switch and the fan motor itself. You can test them separately.

Thanks, that's helpful. How did you or your mechanic test the thermal switch and fan motor? What steps did you take to diagnose them?

My mechanic used a multimeter to check the thermal switch's continuity at different temperatures. They powered the fan motor directly to see if it would spin. Given your Toyota's mileage and the symptoms, check those before focusing on the speed sensor. I'd suggest a workshop visit.

Thanks for the explanation. I'll get the thermal switch and fan motor checked before replacing the speed sensor. It's best to check everything first. It was the speed sensor and cost 250€ to repair.