Coolant reservoir almost empty

Hi, this is my first post plz go easy on me lol

I had a 2nd gen (2014) tacoma and it was recently totaled so I got a used (very used, 208k miles) 2002 tacoma v6.

Literally the day after I bought it, my check engine light came on (fml) and also it sounded like it was having a hard time accelerating. So I went to Autozone to test it, code came back: replace throttle position sensor so I bought the part and opened the hood to replace it when I noticed the coolant reservoir was practically empty. Like an inch of fluid with what looked like a little dirt inside... I havent replaced the sensor bc it doesnt seem like it's the right one but I'm curious if maybe the check engine light is coming on because of the low coolant.

I'll be honest I know close to nothing about cars, but I want to start to learn.

Is it dangerous (for the truck) for me to drive it like this? I have a tow truck coming in the morning to take to my mechanic just in case but I can cancel it if it would be safe to drive..

 

You're ok to add water to the coolant reservoir and drive it for now. It should be checked before the freezing weather gets here to make sure the fluid is good. If not, a flush and fill will be needed.
The sensor is easy to replace, back of the motor, two screws and a harness plug.

 

I'll be pleasantly surprised if that Vato Zone TPS works like it's suppose to,,,,,