Possible Causes & Corrections

WARNING: This page does not describe the selected car, but rather 19 other vehicles, including the 2003 Hummer H2, 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 GMC Sierra, and 2003 GMC Savana Special. However, it is still accessible from the selected car via links, so may be relevant.

Check the following items:

Search for bulletins.
Verify that PCM grounds are clean, tight and in the proper locations.
Remove air filter element and inspect for dirt or for restrictions.
Inspect both injector fuses for being open. An open injector fuse causes 4 ignition coils and 4 injectors not to operate. Replace fuse. Inspect the ignition coil circuits and injector circuits for an intermittent short to ground.
Inspect for incorrect fuel pressure. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.8L, 5.3L & 6.0L "C", "G", "H", "K", "N", "S" & "T" SERIES - FLEX FUEL & GASOLINE article.
Inspect for a restricted fuel filter, contaminated fuel, or improper fuel pressure. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.8L, 5.3L & 6.0L "C", "G", "H", "K", "N", "S" & "T" SERIES - FLEX FUEL & GASOLINE article.
Inspect for a contaminated fuel condition.
Inspect cause for engine to run rich: Water intrusion in HO2S connector, engine oil contaminated by fuel, EVAP canister purge condition, incorrect fuel pressure, leaking fuel pressure regulator, leaking fuel injectors, inaccurate MAF sensor, blockage on MAF sensor inlet screen, vacuum hoses that are split, kinked or improperly connected, air intake duct that is collapsed or restricted, or air filter that is dirty or restricted.
Inspect cause for engine to run lean: Water intrusion in HO2S connector, exhaust leak between HO2S and engine, vacuum leaks, incorrect fuel pressure, restricted fuel injectors, inaccurate MAF sensor, fuel contamination, or vacuum hoses that are split, kinked or improperly connected.
Use a scan tool in order to monitor the Knock Sensor (KS) system for excessive spark retard activity. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C", "K" & "N" SERIES - FLEX FUEL & GASOLINE article or DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L EXPRESS & SAVANA - GASOLINE article.
Verify that both fuel injector fuses are not open. An open fuel injector fuse causes 4 ignition coils and 4 fuel injectors not to operate. Inspect ignition coil circuit and injector circuits for an intermittent short to ground.
Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as water is applied.
Inspect for proper ignition voltage output with Spark Tester (J-26792).
Remove spark plugs and inspect for correct heat range, wet plugs, cracks, wear, improper gap, burned electrodes or heavy deposits.
An improper spark plug gap will cause a driveability problem. Gap spark plugs using a wire gauge gap tool.
Determine the cause of fouling before replacing spark plugs.
Monitor the Misfire Current Counters while driving the vehicle within the conditions that the misfire occurred. If a misfiring cylinder can be located with a misfire, use DTC P0300 diagnostic procedures for diagnosis. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C", "K" & "N" SERIES - FLEX FUEL & GASOLINE article or DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L EXPRESS & SAVANA - GASOLINE article.
Inspect for loose ignition coil grounds.
Verify that the engine coolant temperature is not greater than 266°F (130°C). This condition causes the PCM to operate in Engine Coolant Over Temperature - Fuel Disabled Mode. While in Engine Coolant Over Temperature - Fuel Disabled Mode, the PCM will disable the fuel injectors to 4 cylinders at a time to keep engine temperatures from reaching damaging levels. The driver may perceive the Engine Coolant Over Temperature - Fuel Disabled Mode as a lack of power, miss or rough idle. If vehicle operates in this condition, diagnose engine overheating.
Inspect for excessive oil in the combustion chambers. May be caused by leaking valve seals.
Test for low cylinder compression. See CYLINDER COMPRESSION PRESSURE under MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.8L, 5.3L & 6.0L "C", "G", "H", "K", "N", "S" & "T" SERIES - FLEX FUEL & GASOLINE article.
Inspect for incorrect basic engine parts. Inspect camshaft, cylinder heads, pistons, etc.
Inspect for excessive crankshaft end play that will cause the CKP sensor reluctor wheel to move out of alignment with the CKP sensor. This could result in a no-start, a start and stall, or erratic performance.
Inspect exhaust system for possible restrictions. Inspect exhaust system for damaged or collapsed pipes. Inspect the mufflers for heat distress or internal failure. Inspect for plugged catalytic converters.
Inspect transmission Torque Converter Clutch (TCC) for proper operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.