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For a detailed look at the operating parameters that can set various fault codes, Click Here to view a PDF file on GM 4.6L diagnostic parameters.
OXYGEN SENSOR REPLACEMENT TIPS
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Misfire Diagnosis
If an emissions problem is being caused by an engine misfire, the OBD II lamp may flash as the misfire is occurring. But the lamp will not come on the first time a misfire problem is detected. It will only come on if the misfire continues during a second drive cycle and sets a P0300 series code.
A P0300 code would indicate a random misfire (probably due to a vacuum leak, open EGR valve, etc.). If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring.
Unfortunately, OBD II won't tell you why the cylinder is misfiring. That you have to determine by doing more diagnostic tests once you've isolated the misfire to a particular cylinder. The cause could be a fouled spark plug, bad spark plug wire, weak ignition coil, dirty or dead fuel injector, or a burned exhaust valve.
Random misfires that jump around from cylinder to cylinder will also set a misfire code (P0300). The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the air flow sensor, or an EGR valve that is stuck open. |
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