There is a switch in the cylinder head that operates the temp light.Either it is bad or the cluster is bad.You should take an actual reading in the radiator when it's on.Be careful run it with the cap off until the light comes on and then check it.Don't open the cap on a hot engine you will get burned.On the egr there is a solenoid that the vacuum hose comes from.That's what's probably bad.If the thermometer reads over 240f replace the head gasket it's about all that's left.
Master technician
ASE Master Technician also L1 Advanced Engine Performance Specialist