P0303 2005 Nissan Sentra -

Question

Replaced everything coils, wires, plugs. checked compression everything is good. no vacuum leaks. Still get PO303 code after driving 50 miles. What else could it be?
Car fails to start sometimes when it sits all day, it takes 3 tries before it starts.

Answer 1

Hi there,

Most common issue is the head gasket. Pressure test the cooling system at 16 psi for an hour, then pull #3 and look for coolant on top of the piston. If there is a puddle on top, replace the head gasket.