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I purchased a 99 Suburban in March and it ran perfectly for the first 2 months (March and April). I am actually not sure if it is a 1500 or 2500, however I could not submit my question without picking one. I live in Charleston, SC, and now that the weather has gotten hotter and more humid (85+ degrees), I have had numerous occasions where my truck will start and immediately cut off, or not even turn over at all. I have not noticed a direct correlation where I can actually predict a failed start will occur after the security light comes on and stays on while driving, however every time I have had a failed start incident, the security light will start flashing. I HAVE noticed a direct and distinct correlation between the outside temperature and the likely hood of a failed start. I have had the ignition cylinder replaced, and that seemed to solve the problem for a couple of weeks, however the problem is back and worse than ever. Up until this past weekend, I had always been able to eventually get the truck started. Every time I would experience a failed start, I would bring the truck over to my mechanic to be looked at the next morning. Unfortunately by the time I would get the truck to him, it would start normally and not give any diagnostic codes indicating a problem. I've seen a lot of mixed information on line concerning these systems and am looking for any sort of guidance to help us diagnose and solve this problem for good.
My 99 Suburban would run for half a second and shut off... I thought it was the fuel pump... When it acted up, i shut the key off and tried again. When it wouldn't start I shut the key right off. Meanwhile I got out and tried jumping the fuel pump relay, got back in and it started. Drove home fine, put the relay back in and it ran fine again... thought yep its definitely a fuel pump. A few days later it acted up again. After playing with the relay it started again. So I replaced the fuel pump. A few days later it acted up again. Ran half a second and shut off... this time I left the key on and noticed the security light was flashing... had I left the key on long enough when it didn't start before, I could have saved myself the cost of a fuel pump. I got a new key from GM (non chip type) saw it had more teeth than my old one, aND it worked fine for a few days, then back to running half a second and shutting down. Just for fun I coated my key with graphite lube and worked my new key in and out and on and off... I'm on my third week with no problems. I don't know for sure that my problem is fixed but so far so good.