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Grand Rapids, MI
It's the only coolant attached to the bottom of the radiator.
Here is some info abou both codes: http://repairpal.com/OBD-Code-P0135-and-P0155 http://repairpal.com/OBD-Code-P0300
Sounds like a pressure sensor or gauge problem. It's always good to start by checking the oil pressure in the engine just to rule that out, then look at the rest of the system.
Have you verified that you are getting ignition spark at the plugs? Do you have fuel pressure?