Siena incorrect temperature display

I had something similar on my Siena. Those symptoms sound like a cooling system problem. The ECU uses temperature sensors to manage engine functions. Incorrect readings can trigger the check engine light and affect warm-up times. Have you checked the coolant level? Also, is the radiator grille physically damaged or blocked by debris inside the grille itself?

Coolant level is fine, I did check that first. No visible damage to the grille either, just looks normal. When you say 'inside', do you mean between the grille and the radiator itself? How would I check that properly?

Yes, between the grille and radiator. Road debris, leaves, anything like that can get trapped there and restrict airflow. It's worth taking a look; sometimes it's hard to spot from the outside. However, given the other symptoms, especially the check engine light, it might also be a defective fuse for the radiator fan. Honestly, with those combined issues, a workshop visit is probably the best bet.

You were right, I took it to a workshop, and it turned out a fuse for the radiator fan was defective. Apparently that restricted the cooling which caused all the errors. Repair cost was 52€. All fixed now!