What do these codes mean PO128, PO300 and PO440?

Good evening,

The 128 is for the thermostat. It looks like it may be stuck open not allow the engine temperature to reach normal operating temperature. I would replace the thermostat.

https://www.2carpros.com/articles/how-an-engine-thermostat-works

https://www.2carpros.com/articles/replace-thermostat

The 300 is for a misfire. The most common cause is low fuel pressure from a bad fuel pump. I would check the actual pressure to be sure it is working correctly. I attached guides for you to follow as well. You can rent a tester at a parts store.

Fuel System Pressure

Key On Engine Off 53-59 PSI.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/how-to-replace-an-electric-fuel-pump

The 440 is for the canister vent valve in the emissions. It is stuck open causing a large leak. I posted the location and procedure below.

I attached the procedures below for you. of the fuel pump and thermostat.

Roy

You are welcome.

Always glad to help.

Roy