2005 gt mustang overheating sensor/failsafe mode

2005 GT Mustang – Coolant Temp Errors & Limp Mode Issues (Bama Tuner Related)

Hey everyone, I’m having a strange issue with my 2005 GT Mustang, and I’m hoping someone can point me in the right direction. Lately, I’ve been getting engine coolant temp errors, and I’m having a tough time figuring out what’s causing it.

Here’s what’s happening:

  • As soon as I turn the key to the "on" position (before even starting the car), the car immediately goes into fail-safe mode.
  • The engine temp gauge spikes all the way to the max, even though the engine is cold and hasn’t been started yet.
  • This puts the car into limp mode.
  • Another weird thing: when my Bama tuner is connected during this, it shows the tuner as "unmarried" and not married to the car, even though I know it was married before.

I’ve already tried the following:

  • Resetting the battery
  • Checking the grounds
  • Looking for any obvious electrical issues

Has anyone encountered something like this? Could this be an issue with the coolant temperature sensor, wiring, or maybe the PCM? I’m kind of stuck here and could really use some help from anyone who’s had a similar problem or knows what might be going on.