Mike's Workshop Manuals: Service manuals for every vehicle
Home >> Chevrolet >> 1997 >> Venture Base, Van Passenger Extended >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P0172 - Fuel Trim System Rich >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the BASIC TESTING article. After performing OBD system check, go to next step.
  2. If any other DTCs are set, diagnose DTCs as necessary before proceeding. If no other DTCs are set, go to next step.
  3. Start and warm engine to normal operating temperature. Ensure system is in closed loop. Using scan tool, select ENG 1 data list. Observe L.T. FUEL TRIM and S.T. FUEL TRIM. If L.T. FUEL TRIM is about -16 percent and S.T. FUEL TRIM is about -11 percent, go to step 5). If fuel trim is not as specified, go to next step.
  4. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info for DTC P0171 until DTC P0171 test runs. If scan tool indicates FAILED THIS IGN, go to next step. If scan tool does not indicate FAILED THIS IGN, see DIAGNOSTIC AIDS.
  5. Inspect air filter element. Replace as necessary. After replacing air filter element, go to step 21). If air filter element is okay, go to next step.
  6. Check for collapsed or restricted air intake duct. Repair as necessary. After repairs, go to step 21). If air duct is okay, go to next step.
  7. Inspect throttle body inlet screen for damage or blockage. Repair as necessary. After repairs, go to step 21). If inlet screen is okay, go to next step.
  8. Start engine and check idle quality. If idle is high or rough, go to next step. If idle is okay, go to step 11).
  9. Allow engine to idle. Using scan tool, observe IDLE AIR CONTROL display. If counts are greater than 100, go to step 11). If counts are not greater than 100, go to next step.
  10. Turn ignition off. Inspect throttle body bore, throttle plate and IAC passages for coking and foreign objects. Repair as necessary. After repairs, go to step 22). If no problem is found, go to next step.
  11. Check Idle Air Control (IAC) valve operation. See the SYSTEM/COMPONENT TESTS article. Repair as necessary. After repairs, go to step 21). If IAC valve is functioning properly, go to step 13).
  12. Disconnect vacuum hose from fuel pressure regulator and check hose for presence of fuel. If fuel is present, replace fuel pressure regulator. After replacing pressure regulator, go to step 21). If fuel pressure regulator is okay, go to next step.
  13. Turn ignition on. Monitor TP angle display on scan tool while slowly depressing accelerator pedal. If TP angle display increase steadily from 0-100 percent (wide-open throttle), go to next step. If TP angle display does not increase as specified, go to step 19).
  14. Disconnect MAF sensor connector. Start engine and allow it to idle. Ensure system is in closed loop. Using scan tool, observe ST FUEL TRIM and LT FUEL TRIM display. If both values change to about zero percent, go to step 21). If one or both values do not change to about zero percent, go to next step.
  15. Perform BASIC FUEL SYSTEM CHECKS in the BASIC TESTING article. Repair fuel system as necessary. After repairs, go to step 22) If fuel system is okay, go to next step.
  16. Check fuel evaporation system for proper operation. Ensure canister purge solenoid is functioning properly. See the SYSTEM/COMPONENT TESTS article. Repair as necessary. After repairs, go to step 21). If fuel evaporation system is functioning properly, go to next step.
  17. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article. Repair as necessary. After repairs, go to step 21). If no problems were found, go to next step.
  18. Visually and physically inspect HO2S 1 for silicon contamination (White powdery deposits). If contamination is evident, replace sensor. After replacing sensor, go to step 21). If sensor is okay, see DIAGNOSTIC AIDS.
  19. Check TP sensor mounting screws. Tighten or replace screws as necessary. If screws are okay, replace TP sensor. After replacing sensor, go to step 21).
  20. Replace MAF sensor. After replacing sensor, go to next step.
  21. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info until DTC P0171 test runs. If scan tool indicates FAILED THIS IGN, repeat step 2). If scan tool does not indicate FAILED THIS IGN, repair is complete.
scientia non olet · About Mike's Workshop Manuals