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Home >> Chevrolet >> 2001 >> Lumina >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 3.1L >> Diagnostic Tests >> DTC P0420: Catalyst System Low Efficiency >> Code Enable Criteria

Code Enable Criteria

PCM will run diagnostic for this DTC when the following conditions are met:

  1. Meet conditions for engine warm-up. Use scan tool catalyst data list to verify the following:
    • No EGR, ECT, MAF, TP, IAT, MAP, CMP, CKP, VSS, EVAP, HO2S IAC, fuel trim or fuel injector related DTCs are set.
    • Engine has been running longer than 10 minutes.
    • ECT is between 169-255°F (76-124°C).
    • Barometric pressure (BARO) is more than 75 kPa.
    • System is in closed-loop.
    • IAT is greater than - 4°F (- 20°C) and less than 212°F (100°C).
    • Battery voltage is greater than 10.7 volts.
  2. Warm up catalyst as follows:
    • Fully open hood.
    • Ensure transmission is in Park.
    • Set parking brake.
    • Press and hold service brake.
    • Each time engine is started, diagnostic can run up to 18 times. After 10-minute run time, and before diagnostic runs the first time, engine must run an additional 5 minutes between 1500 and 2500 RPM. For any additional tests on same ignition cycle, engine must run for one minute between 1500 and 2500 RPM.
    • To activate diagnostic, return to idle and shift transmission into Drive.
  3. Test catalyst as follows:
    • Ensure transmission is in Drive.
    • Within 60 seconds, air/fuel ratio will go rich (less than 14.1:1) for up to 8 seconds, then may go lean (more than 15.3:1) for up to 10 seconds.
    • Using scan tool, check if DTC P0420 ran and passed, or failed this ignition cycle.

DTC will set when PCM determines that the catalyst's oxygen storage capacity is below a threshold considered acceptable.

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