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 for the following items:

Search for bulletins.
Inspect PCM grounds for being clean, tight and in the proper locations.
Verify the driver understands the operation of the transmission Torque Converter Clutch (TCC) and A/C compressor operation as explained in the owner's manual. Inform customer how the TCC and A/C clutch operates.
Inspect HO2S. The HO2S should respond quickly to different throttle positions. If they do not, inspect HO2S for silicone or other contaminates from fuel or use of improper RTV sealant. The sensors may have a White, powdery coating and result in a high but false signal voltage rich exhaust indication. The PCM will then reduce the amount of fuel delivered to the engine causing a severe driveability problem.
Inspect the Mass Airflow (MAF) sensor connections. Repair or replace damaged terminals.
Test 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. 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 article.
Inspect for a contaminated fuel condition.
Verify that each injector harness is connected to the correct injector or cylinder. Relocate injector harnesses as necessary.
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 Mass Airflow (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.
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
Test 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, use the 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 above 266°F (130°C). This condition causes PCM to operate in Engine Coolant Over Temperature - Fuel Disabled Mode. While in Engine Coolant Over Temperature - Fuel Disabled Mode, the PCM turns fuel OFF to 4 cylinders at a time to keep engine temperatures from reaching damaging levels. The driver may perceive this condition as a lack of power, miss or rough idle.
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.
Visually and physically inspect vacuum hoses for splits, kinks, and proper connections and routing as shown on the underhood Vehicle Emission Control Information label.
Inspect the transmission Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS. A TCC applying too soon can cause the engine to spark knock.