Question about 2003 Hummer H2
First start by making sure that the spark plugs are AC Delco plugs or other WILL trigger a P0300. If these are good, the next thing to check is the coolant temperature sensor(ECT). If this is problematic, it will cause too much fuel to be delivered and misfires to occur on all cylinders.
Posted on May 09, 2010
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Posted on Jan 02, 2017
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P0300....Random/Multiple Cylinder Misfire Detected
ask local mechanic to have a look for you ,could just be a cold damp engine or snow blown under the bonnet
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