The problem of the car engine P2173 Code can be serious and spark knock or detonation, is a sort of combustion produced by the accumulation of too much heat and pressure in the engine’s combustion chamber. When this happens, you should be able to hear a metallic knocking or pinging noise. A small amount of detonation usually will not reason key injury, but weighty knocks or prolonged explosion can cause serious harm to your parts. It can punch holes in your pistons, crush rod bearings, crack rings, blow head gaskets, and pound out piston ring grooves. Prolonged pinging noises are a sure motive for worry.