I don't see that AHT error code in the service manual. However the error code ending Tp0P is for the power supply sensor. It says - verify that the single pin connection on the top edge of the power supply is present and securely plugged in. If this sensor wire is not connected correctly the CPU fan will run at full speed. This seems to be a common problem. None of the sensor apps like iStats show the PSU temperature. They show all the other temperature sensors reading normal with the CPU fan speed running over 3000rpm. If this connection is OK in your machine, maybe you new PSU has a bad sensor.