What is the po452 error code refering to? - 2007 Jeep Grand Cherokee Overland

Maybe.
Codes 121 and 122 are for the throttle position sensor circuit.
Code 400 is EGR and codes 449 and 452 are for the EVAP system.
Code 1639 is for a problem with the 5 volt reference circuit from the engine computer.
The throttle position sensor could be failing which could prevent the gas pedal from working. And the 5 volt reference problem could shut down the computer which would kill the engine. EGR is an emissions component and EVAP is the system that vents gas fumes from the gas tank.
Codes are only a guide for a mechanic to troubleshoot the circuits involved. They do not mean a component is faulty.

Why would they you have a PO452

You wouldn't have a code if the evap monitor
had not run

Here's a link to your P0452 code.

PO440-EVAP SYSTEM NO FLOW DURING PURGE.CODE PO PO452 - FUEL TANK PRESSURE SENSOR CIRCUIT LOW INPUT.

P0452 evap control pressure low, P0 446 evap vent contol circuit. Becuase you have P0452 you are dealing with a eletrical issue whether you have positive tank pressure or negative pressure, The tool for this is a volt meter.452 happens when you positive pressure and the FTP reads less than 0.1 volts.You need to jump the signal and the reference and monitor the take parameter on a scan data you should read reference voltage.Now if you dont have a scan data tool. inspect the wire for any breaks or shorting 2 thing of concern broken wire to the FTP or a ECM is needed.

your code PO452 comes up............Evaporative emission control system, pressure sensor low imput.

CODE PO452 IS FUEL TANK PRESSURE SENSOR CIRCUIT LOW INPUT CONDITIONS.YOU COULD HAVE A FAULTY FUEL TANK PRESSURE SENSOR.

both codes point to the fuel tank evap pressure sensor. High and low input faults.
Try clearing the codes first and seeing if they come back

You may have a vacuum leak, cracked or open vacuum line or faulty sensor.

CODE PO452 FUEL TANK PRESSURE SENSOR CIRCUIT LOW INPUT CONDITIONS.YOUR FTP OR FUEL TANK PRESSURE SENSOR FAILED. PO651 5 VOLT REFERENCE 2 CIRCUIT MALFUNCTION CONDITIONS.POSSIBLE CAUSE 5 VOLT REF.CIRCUIT IS SHORTED TO CHASSIS OR SENSOR GROUND.OR 5 VOLT REF CIRCUIT TO MAP OR TP SENSORS CIRCUIT IS SHORTED TO B+.ALSO YOUR PCM HAS FAILED.YOU PROBABLY NEED TO TAKE IT TO DEALERSHIP.THEY HAVE DIAGNOSTIC EQUIPMENT TO CHECK SENSORS AND PCM FAILURE.

you might try unhooking the battiey for 20min both + and - posties cuz that will force the computor to have to resest only if you have addressied the fuel pressure problem which taht would most likly be your filter which isn't all that much