Can't find coolant leak, check engine light on, please help

Did you replace the pump yourself? I suspect the coolant wasn't filled properly during the refill process. It should be nearly full now after adding half gallon.

You should bleed all the air out and make sure your heater works

 

If there is no obvious drips, then somehow it is being consumed inside the engine.
Which could mean you have a head gasket leak. (Heads often get warped if they are overheated.)

Is there white "smoke" coming out of your tailpipe?

You may want to have it checked out at a mechanic shop.
They can pressure check for leak.

 

how many miles on her?

 

The capacity of the engine coolant system for 2G North American Prius is 9.1 US quarts. So the problem is significant, and if you don't see any fluid actually leaking out then the engine must be consuming it.

1. How many miles on the odometer?
2. It appears that the catalytic converter has also failed since the car logged DTC P0420.
3. Do you see whitish smoke out the tailpipe when you accelerate hard?
4. What does the engine oil look like on the dipstick? If it has a creamy look to it, then coolant is mixing with engine oil.
5. If you see either or both of 3 and 4 above then the engine is dead and you should develop a plan to either replace the engine with a used unit (which might cost $2.5K or so as labor will be the major cost), or else purchase a replacement vehicle.

 

If he waterpump failure caused an engine overheat event it probably damaged the head
Coupled with the fact that after the repair the coolant was not bledd properly which also results in an overheat because air is trapped in the highest point of the engine the head
You were probably hearing water gurgling under the dash
Which is air in the coolant system

 

Kerry- Are you using the special Toyota Super Long Life coolant, the pink stuff? Sometimes you can see that caked up as pink salts if there is a leak usually by the water pump.