On my 2012 Honda jazz hybrid with 103,000 KM on it I just changed all eight spark plugs. Frankly when I went to tighten down the back side second from the left I wasn't 100% sure I tightened the plug enough. The car is running fine however it's been a week and I'm still getting lousy gas mileage. (Also changed my O2 and air filter). I ran my OBD and sure enough a PO356 showed up. Apparently that's "number 6 cylinder", but since it's a four-cylinder car do I take it that it's the sixth spark plug and coil? meaning back left side second one over?? (As I suspected might be a problem). Pain in the neck to take off the wipers, the plastic cowling, the metal shelf etc. Thanks!