DTC Code P0300 - Multiple Random Cyliner Misfire - Hummer Forums - Enthusiast Forum for Hummer Owners

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Old 07-20-2007, 12:00 AM
Join Date: Jan 2007
Posts: 42
Default DTC Code P0300 - Multiple Random Cyliner Misfire

Hey Guys,

Well, my H2 has been in the shop now for almost 2 weeks. I won't go in to the details, but it was running very poorly, and I was getting a DTC code of P0300, "random multiple cylinder misfire". I took it in to the dealer to have them re-flash my ECM back to a stock tune (it had been modified), and the dealer fried the ECM computer. They refused to take responsibility for it, so I told them where they could stick it, and had a tow truck hall my H2 out of their shop. (Needless to say, I am not invited back there again)

I got a new ECM from a place called Wester's Garage (www.ecmprogrammer.com) and installed it. Super shop by the way!! The truck runs again, but still doesn't run properly.

It went in to a local shop that I once worked for many years ago, and whom I feel I can trust. They have been working on diagnosing the problem, but are not having much luck. When attached to the scope, monitoring each cylinder, it appears that different cylinders will randomly shut down, and then start working again.

Has anyone experienced a problem similar to this? Any information might lead to an answer, and will be greatly appreciated.


2003 H2, MagnaCharger M90 Sidemount Supercharger, 18" Foose Wheels
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Old 08-01-2010, 12:29 AM
Junior Member
Join Date: Jul 2010
Posts: 1
Default DTC code PO 300

did you ever get to the bottom of the the issue? my Modded truck just started to do the same thing?

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07, 2003, code, codes, cyclinder, cylinder, dtc, h2, h3, hummer, misfire, multiple, p0300, random, reflash

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