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Home >> GMC >> 1997 >> Forward Control 4.3 W, L35, Automatic >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 11 (Engine Controls - Tests W/Codes - 7.4L (P Series)) >> Diagnostic Trouble Codes >> DTC P0146 - Ho2S Insufficient Activity Bank 1, Sensor 3 >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different variant/trim than selected.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the F - BASIC TESTING - 7.4L article. After performing OBD system check, go to next step.
  2. Connect scan tool. Warm engine to normal operating temperature. Run engine at greater than 1200 RPM for 2 minutes. If scan tool indicates closed loop, go to step 5). If scan tool does not indicate closed loop, go to next step.
  3. Turn ignition off. Disconnect HO2S harness connector. Connect jumper wires between ground, and HO2S ground and HO2S signal circuits of HO2S connector (VCM side). Turn ignition on, with engine off. Monitor HO2S voltage using scan tool. If HO2S voltage is less than 0.2 volt, go to step 7). If HO2S voltage is not less than 0.2 volt, go to next step.
  4. Remove jumper wires and reconnect HO2S connector. Turn ignition off. Disconnect Blue VCM connector. Using test light, probe VCM connector HO2S signal circuit to battery voltage. If test light illuminates, go to step 6). If test light does not illuminate, go to step 9).
  5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
  6. Check for open in HO2S signal circuit. If signal circuit is open, go to step 11). If circuit is okay, go to step 8).
  7. Check for poor connection at HO2S. If connection to HO2S is faulty, go to step 11). If connection is okay, go to step 10).
  8. Check for poor connection at VCM connector. If connection is faulty, go to step 11). If connection is okay, go to step 12).
  9. Repair open in HO2S ground circuit. After repairs, go to step 13).
  10. Replace HO2S. After replacing sensor, go to step 13).
  11. Repair circuit as necessary. After repairs, go to step 13).
  12. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, 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 P0146. 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.
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