I have the same problem. Unplugging the EFE heater connector solves the fuse-blowing issue but the P1250 DTC will re-appear as soon as the engine temp is warm, when the EFE-off signal voltage is unable to be measured. My EFE heater falls in the middle of specified normal electrical resistance (it is 1.6 ohms at 68 degrees F), but I suspect the problem is that the EFE heater is shorted to ground through a faulty TB gasket; this would explain the PTC fuse blowing as soon as you start the engine. I am ordering a new EFE upper and lower gasket, which are about $10, a lot cheaper than assuming a need to replace the $300 EFE heater.
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