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Ron Z.
Ron Z., - GMC Tech -
Category: GMC
Satisfied Customers: 18773
Experience:  18+yrs experience. State Inspector & GMC Diagnostics/Repair
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Check JA: Sometimes things that you think will be really

Customer Question

JA: Sometimes things that you think will be really complicated end up being easy to fix with GMC. The GMC Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so he can help you best.
Customer: Check engine started flashing on my 2009 GMC Sierra 5.3
JA: Are you hoping to fix this yourself?
Customer: If it's something I can do yeah.
JA: Is there anything else the GMC Mechanic should be aware of about your GMC?
Customer: The Check engine light has been on for over a month
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the GMC Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: GMC
Expert:  Ron Z. replied 1 year ago.
When the Check Engine Light flashes, this is the sign for "Random Cylinder Misfire". This means that one or more of the cylinders is not firing correctly. This can be caused by a few different things- lack of spark, lack of fuel, incorrect fuel/air mixture, low cylinder compression, etc. Given the year of the vehicle, I'd lean more towards a problem with worn spark plugs or possibly low fuel pressure due to a failing fuel pump. Best place to start here is by having the Diagnostic Trouble Codes (aka "P-Codes") scanned from the on-board computer and see if there are any other codes stored besides the P0300-Random Cylinder Misfire. If there are no other codes stored in the on-board computer, best place to start is by inspecting the spark plugs. Inspect for any cracks i nthe body and/or wear of the diode. If there are any doubts, replace all the spark plugs. If the spark plugs look good, test fuel pressure. Correct fuel pressure is between 50-60 psi with key-on/engine-off. If below specs, the fuel pump will need to be replaced (no external fuel filter on this vehicle). If the spark plugs and fuel pressure are good and/or there are other codes retrieved from the scan, then further testing will need to be done. You can have these p-codes read FREE (except in California) at any local "big chain" part store (ie. AutoZone, PepBoys, Advanced, etc). If my answer has helped you, please help me and rate or accept my answer.Rating or accepting my answer does not cost you extra. It allows me to be credited for this Q&A. If you cannot rate or do not see where to rate, please let me know! You can ask follow-up questions after you rate or accept. Thank-you!
Expert:  Ron Z. replied 1 year ago.
Expert:  Ron Z. replied 1 year ago.