I have 2011 duramax, a week ago my check engine light came on so I plugged in my scanner and gave me a glow plug for #5 cylinder. I tested it and it was bad. I live in a small town so I was only able to purchase 4 glow plugs, so I only replaced the glow plugs on the odd cylinders. Yesterday my check engine light came on again and the code for that was #2 glow plug. Is this common? Is there a relay bad? Haven't checked that glow plug yet waiting for new ones to show up. Is there something else wrong cause the truck only has 50000 miles?