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HOMESERVICE MANUALSCHEVROLET1998SUBURBAN K2500, 7.4 J, PART TIMEREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - TESTS W/CODES - 7.4LDIAGNOSTIC TROUBLE CODESDTC P0420 - TWC SYSTEM LOW EFFICIENCY BANK 1DIAGNOSTIC PROCEDURES
1998 Chevrolet Suburban K2500, 7.4 J, Part Time

Diagnostic Procedures

1998 Chevrolet Suburban K2500, 7.4 J, Part TimeSECTION Diagnostic Procedures
  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK , then go to next step.
  2. Check if any MAP sensor, HO2S, misfire, fuel trim, VSS or ECT sensor DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
  3. Check for the following conditions:
    • Ensure TWC system is original equipment installed by manufacturer.
    • Check TWC system for damage (i.e., dents, severe discoloration caused by excessive temperatures, holes).
    • Ensure internal converter rattle (caused by damaged catalyst) is not present.
    • Check exhaust system between TWC system and rear converter flange for leaks, damage, or loose or missing hardware.
    • Ensure HO2S bank 1, sensor 27 is secure, and pigtail and wiring is not damaged or contacting exhaust.

    On all models, if a problem is found, go to step 9). If no problem is found, go to next step.

  4. Check all VCM grounds. If a problem is found, go to step 9). If no problem is found, go to next step.
  5. Check all sensor grounds. If a problem is found, go to step 9). If no problem is found, go to next step.
  6. Check for intermittent open in catalyst monitored HO2S signal and ground circuits. If a problem is found, go to step 9). If no problem is found, go to next step.
  7. Check for intermittent short to ground on catalyst monitored HO2S signal and ground circuits. If a problem is found, go to step 9). If no problem is found, go to next step.
  8. Replace TWC system. Check for possible misfire (DTC P0300) or engine mechanical problem. After repairs, go to step 10).
  9. Repair problem as necessary. After repairs, go to next step.
  10. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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).
  11. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test.
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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.