Diagnostic Aids

WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

Check for the following conditions:

Incorrect CKP system variation data stored in the PCM. Run the CKP System Variation Learn Procedure using scan tool. See CRANKSHAFT POSITION SENSOR under PROGRAMMING.
System grounds. Ensure that all connections are clean and properly tightened.
Damaged accessory drive belt or driven accessory. A damaged serpentine belt or belt driven accessory can cause engine load variations sufficient to set a misfire DTC.
Fuel pressure. Perform a fuel system pressure test. A malfunctioning fuel pump, plugged filter, or malfunctioning fuel system pressure regulator will contribute to a lean condition. See BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
Fuel injectors. See FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.3L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
Contaminated fuel.
Extended idle. Excessive Open Loop operation caused by extended idling or short trip driving may leave deposits on the Heated Oxygen Sensors (HO2S). The deposits cause oxygen sensors to respond slowly to exhaust oxygen content, affecting fuel control and causing a misfire to be indicated at idle. This condition is not permanent. To determine if this condition is causing the DTC P0300 to be set, review the Freeze Frame/Failure Records data for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described did not cause the DTC P0300 to set. If the DTC P0300 occurs at idle or very low engine speeds and at engine coolant temperatures less than 176°F (80°C), the condition described is very likely the cause of the DTC P0300 being set. The deposits on the heated oxygen sensors can be eliminated by operating the vehicle fully warm at mass air flows more than 15 g/s.
Running the vehicle low on fuel. This DTC may set if the vehicle misfires while running out of fuel. If no misfire is currently present, but the History Counters indicate random misfire was once present, ask if the vehicle has been run out of fuel. If this is the case, no further repair may be necessary.

NOTE: If the level of misfire was sufficient to cause possible catalyst damage, if the MIL was flashing, ensure that the DTC P0420 test is completed and passed after verifying the misfire repair. See DTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1) .

If the condition is intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.