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HOMESERVICE MANUALSCHEVROLET1996TAHOE 2D UTILITY, 6.5 SREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - TESTS W/CODES - GASOLINEDIAGNOSTIC TROUBLE CODE TESTSDTC P0172 - FUEL TRIM SYSTEM RICH BANK 1DIAGNOSTIC PROCEDURES
1996 Chevrolet Tahoe 2D Utility, 6.5 S

Diagnostic Procedures

1996 Chevrolet Tahoe 2D Utility, 6.5 SSECTION Diagnostic Procedures
  1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
  2. Check for the following conditions:
    • Air intake duct collapsed or restricted.
    • Air filter plugged.
    • Throttle body coking or objects blocking IAC passage, if a low or unsteady idle is being experienced.
    • Fuel pressure regulator for proper operation. See appropriate BASIC TESTING article.
    • TP sensor for loose or missing mounting bolts. Monitor TP sensor voltage using scan tool while slowly opening throttle. Voltage should increase steadily and evenly from closed throttle voltage (.5 volt) to wide open throttle voltage (4.5 volts). If voltage is not as specified, replace TP sensor.

      If a problem was found, go to step 8). If a problem was not found, go to next step.

  3. Connect a fuel pressure gauge to fuel rail fitting. Turn ignition off for 10 seconds. Turn A/C off. Turn ignition on. Fuel pump should run for about 2 seconds. It may be necessary to cycle ignition on more than once to obtain maximum pressure. Note pressure with pump running. On CSI models, pressure should be 60-66 psi (415-455 kPa). On SFI models, pressure should be 56-62 psi (385-430 kPa). On all models, when pump stops, pressure may slightly vary, but should hold steady. If pressure is as specified, go to next step. If pressure is not as specified, go to step 11).
  4. Perform injector balance test. See appropriate SYSTEM/COMPONENT TESTS article. If a problem was found, go to step 9). If a problem was not found, go to next step.
  5. Remove HO2S and inspect for silicone contamination (a white powdery deposit on portion of sensor exposed to exhaust stream). If contamination is found, go to step 12). If contamination is not found, go to next step.
  6. Perform canister purge solenoid check. See appropriate SYSTEM/COMPONENT TESTS article. If a problem was found, go to next step. If a problem was not found, see DIAGNOSTIC AIDS.
  7. Repair EVAP system. Install scan tool. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should increase to greater than 100. ST fuel trim value should increase to greater than 94. If values are as specified, go to step 10). If values are not as specified, see DIAGNOSTIC AIDS.
  8. Repair problem as necessary. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should increase to greater than 100. ST fuel trim value should increase to greater than 94. If values are as specified, go to step 10). If values are not as specified, go to step 3).
  9. Replace fuel injector. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should increase to greater than 100. ST fuel trim value should increase to greater than 94. If values are as specified, go to next step. If values are not as specified, go to step 5).
  10. Rich condition is not present. See appropriate TROUBLE SHOOTING article.
  11. Diagnose fuel system. See appropriate BASIC TESTING article. Go to step 13).
  12. Replace HO2S. Go to next step.
  13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0172. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
  14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test. If no DTC's are displayed, system is okay.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.