My port 496 Mag is going into Guardian Mode at 4000+ RPM. I have a Merc scan tool that reads the codes, which is showing "overheat", but the temp guage is never going above 170 degrees. I can run all day under 4000 RPM with no issues. Does anyone know if the Merc Scan tool gives the same code reading for low water pressure as overheat?

The fault should be specific to either an exhaust manifold overtemp (EMCT Overheat) or Engine Coolant overheat (ECT Overheat), or Seapump pressure (Sea Pmp Pressure Low). Each one should set a different Fault code.

You could check system temps with a infrared to confirm the fault(s).

Dave

Bad Sensor possibly sending a false code?????

Dave N/Griff, thanks for the feedback. I know the false code is a possibility. Just trying to rule out some stuff before I haul it to the dealership. Based on Dave's feedback, I'm thinking faulty sensor also. Thanks again!