2010 Prius with possible clogged EGR

congrats and welcome! no warranty from the seller? you'll need a code reader for the engine light, could be as simple as a loose gas cap

 

Two conditions can contribute to low EGR flow and a P0401 code: clogging, and a rutted ski jump in the valve actuator. You might have either one or both. Whoever looks should check for both.

Of course, the extra-simple causes are also worth checking, like something just plain stuck, or an issue in the electrical circuit (which would give P0403 if obvious enough for the car to detect it).

 

Second day? The guy trading it in likely scammed the dealer, who went on to scam you (deliberately or not)

90% of the time you are better off cleaning it yourself to save the money. Only tricky(nightmare) part is the egr cooler bolts

 

One bolt in particular. More accurately, one nut-on-stud, highlighted in yellow:



Make it easier on yourself, remove that nut, and the associated stud, in advance of the main job. It can be done without any other disassembly, and both the nut and stud can be left off permanently. This has the side benefit, of allowing the two studs at the rear of the cooler to remain installed, which in turn helps retain the rear gasket as you pull the cooler out, and retains/aligns the gasket during subsequent reinstall.

At that same prelim nut/stud removal, it's good to "dress rehearsal" the similar nut/stud combo going through the EGR valve, and the bolt at the top EGR cooler bracket: remove them, add a thin/uniform skin of anti-seize (work into the threads with an old toothbrush or similar), and reinstall, slightly shy of torque value.

Also, on the day of the main job, before doing anything else, drain two quarts (or litres) from the radiator bottom spigot, into a clean container (pour it back into reservoir when done). This'll drop the coolant level below the EGR components, avoid virtually all spill when cooler coolant lines are pulled off.

Also, there's no need to disconnect throttle body coolant lines; the throttle body can be lifted off with them attached, tied to the inverter wiring harness.

Then, no nightmares.