Possible Causes & Corrections
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 the following items:
- Low engine coolant level.
- Correct coolant mixture.
- Proper tension on the drive belts.
- Restricted air flow through the radiator or restricted coolant flow.
- Faulty thermostat.
- Inspect for an Engine Coolant Temperature (ECT) sensor that has a shift in value. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
- Drive vehicle at the speed of the complaint. Monitoring the fuel trim will help identify the problem.
- If system is lean, the long term fuel trim will be more than 150 on scan tool.
- Test fuel pressure. Refer to FUEL SYSTEMS BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
- Inspect for a poor fuel quality and a proper octane rating.
- If fuel trim readings are normal and there are no engine mechanical concerns, fill fuel tank with a known-good fuel and re-evaluate vehicle performance.
- Inspect spark plugs for proper heat range and gap.
- Inspect Knock Sensor (KS) system operation.
- Inspect ignition timing.
- Inspect for carbon build up. Remove carbon with a top engine cleaner.
- Test the combustion chamber pressure by performing a compression test. See CYLINDER COMPRESSION PRESSURE under MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
- Test the Torque Converter Clutch (TCC) operation. TCC applying too soon can cause engine to spark knock. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.
- Search for Service Bulletins for calibration updates.