Diesel Engine Water Temperature; Fuel Temperature; Water Temperature (FOR E.F.I.). Engine Coolant Temperature Sensor - Repair or Replace If your Engine coolant temperature sensor has failed, you may notice one of several symptoms: your temperature gauge doesn???t move, your Engine overheats w/o warning, your radiator fans don???t switch on, or they don???t switch off. If your Toyota has any of these symptoms, it's a good idea to let a trained Toyota technician perform an inspection.