Start by checking the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.
The P0300 code means that a cylinder(s) is misfiring or is randomly misfiring. Start by checking for intake leaks, intake gaskets are commonly caused by multi-cylinder misfiring. If no leak is found the next step is to replace the spark plugs. If the problem persists more tests need to be done to diagnose the problem, see "Possible Causes".
There is a Factory Service Bulletin for the following HUMMER models:
2003-2008 HUMMER H2
2006-2008 HUMMER H3
2003-2008 HUMMER Factory Service Bulletin OBDII Code P0300
The cost to diagnose the P0300 HUMMER code is 1.0 hour of labor. The auto repair's diagnosis time and labor rates vary by location, vehicle's make and model, and even your engine type. Most auto repair shops charge between $75 and $150 per hour.
A misfiring cylinder causes slight variations in the rotational speed of the crankshaft. The Engine Control Module (ECM) is able to detect these variations by closely monitoring the crankshaft position sensor signal. The signals of the camshaft position sensors are used to determine which cylinder is misfiring. If the ECM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, the Diagnostic Trouble Code (DTC) will be set. Under certain driving conditions, a misfire rate can be high enough to cause the catalytic converter to overheat, possibly damaging the converter. The Malfunction Indicator Lamp (MIL) flashes when the converter is overheating, damaging conditions are present, and the DTC is set. The DTC will be set when the ECM detects a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed a predetermined value or a misfire rate high enough to cause catalyst damage.
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