Possible Causes & Corrections
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Savana, 2003 Chevrolet Silverado, and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
Check for the following items:
- Ensure driver understands the torque converter clutch operation and A/C compressor operation.
- Test for proper operation of the Vehicle Speed Sensor (VSS). See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 6.0L CHEVY EXPRESS & SAVANA - BI-FUEL & CNG article DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 6.0L SILVERADO & SIERRA - BI-FUEL & CNG article.
- Test for proper operation and performance of the oxygen sensor.
- Inspect for a lean or rich engine condition. Using a scan tool observe the oxygen sensor output while operating the vehicle under the symptom condition.
- Check fuel pressure. See FUEL SYSTEM PRESSURE TEST under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL & CNG article.
- Inspect for proper operation of the CNG fuel injectors. See FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL & CNG article.
- Ensure that manual shut-off valve is fully open.
- Inspect for restricted HPR or in-line filters.