Prius gurus P1452

Never heard of DTC P1452 before, which OBD2 scanner are you using ?

Where in the bay area are you located, maybe someone can offer to scan your vehicle with a toyota hybrid compatible scanner.

You might try tightening the fuel cap until it clicks three (3) times, also try applying some spit or silicon lubricant to the caps o-ring.

 

I don't think that's going to help, but nice if it did. That code related to the fuel tank pressure sensor.

	DTC No.	Monitoring Item	DTC Detection Condition	Trouble Area	Detection Timing	Detection Logic
1	P1452	Pressure sensor voltage low	Sensor output is less than -3999 Pa for 7 seconds.	Fuel tank pressure sensor Connector/wire harness (Fuel tank pressure sensor - ECM) ECM	EVAP monitoring (power switch OFF) Power switch ON (IG)	1 trip

The areas where there could be a problem is in the Trouble Area column.

Full details and workup for this problem are in the repair manual; more info.

 

You'll want to get the techstream working because you need something of that caliber to be able to go into the ECM data to see what the reading is from the fuel tank pressure sensor. That sensor is used to detect if there are any leaks in the evaporative emissions system (fuel tank vapors). The sensor mounts on top of the tank in the right rear corner. It has a 5V supply circuit, a ground, and a signal wire. That signal voltage varies with the amount of pressure or vacuum inside the fuel tank (and emissions system)- it is less than +1/2 psi to -1/2 psi (+4 to -4 pascals) total range. I don't recall the specs on the sensor but the signal would likely be something from around 0.5V to 4.5V. The code indicate that the ECM saw the signal go below its normal range- that can't really be caused by a bad gas cap.

Whoever diagnoses this problem will have to measure what the actual signal voltage is and compare it to the reading by the ecm. If it is wrong then you/they have determine if the fault is the sensor, the wiring (damaged, short to ground, loose connector, open circuit, etc), or inside the ECM.