Diagnostic Procedures

WARNING: This page is about a different car, the 2003 GMC Savana and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

Did you perform the Diagnostic System Check - Alternative Fuels - Engine Controls. If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM.

NOTE: If any DTCs other than P0172 are set, see DIAGNOSTIC TROUBLE CODE DEFINITIONS .

Install scan tool. Start and idle the engine at the normal operating temperature in Closed Loop. Record the long term fuel trim data. Turn the engine off. Turn ignition on, with engine off. Review the Freeze Frame/Failure Records, and record the displayed data for this DTC. If the scan tool indicates that the long term fuel trim is less than -15 percent, go to next step. If the scan tool indicates that the long term fuel trim is more than -15 percent, see DIAGNOSTIC AIDS .
Operate engine at idle. Observe the HO2S parameters using a scan tool. If the scan tool indicates that the HO2S parameter is 200-800 mV and fluctuating, go to next step. If the scan tool indicates that the HO2S parameter is not 200-800 mV and fluctuating, go to step 5.
Turn engine off. Visually and physically inspect the following:
- EVAP lines and components, if equipped, for damage or blockage.
- Mass Airflow (MAF) sensor inlet screen for blockage.
- Vacuum hoses for splits, kinks, and proper connections. See VACUUM DIAGRAMS - EXPRESS & SAVANA article.
- Air intake duct for being collapsed or restricted.
- Air filter for being dirty or restricted.
- Objects blocking the throttle body.
Did you find and correct the condition? If yes, go to step 7. If no, go to step 6.
Turn the engine off. Inspect the HO2S for proper installation. Verify the electrical connectors and the wires are secure and not contacting the exhaust system. Test for continuity between the HO2S signal circuit and the low reference circuit. Did you find and correct the condition? If yes, go to step 7. If no, 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 the following:
- Excessive fuel in the crankcase (KL6 only).
- Proper operation of the gasoline fuel pressure regulator (KL6 only). 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.
- All CNG fuel injectors are functioning properly. See FUEL INJECTOR COIL TEST under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL & CNG article.
- All gasoline fuel injectors are functioning properly. See FUEL INJECTOR COIL TEST under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.8L, 5.3L & 6.0L "C", "G", "H", "K", "N", "S" & "T" SERIES - FLEX FUEL & GASOLINE article.
Did you find and correct the condition? If yes, go to next step. If no, check engine mechanical condition. See appropriate article in ENGINES.

NOTE: After repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.

Using a scan tool, clear the DTCs. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. If the DTC failed this ignition cycle, go to step 2. If the DTC did not fail this ignition cycle, go to next step.
Observe the Capture Info using a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.