Code Enable Criteria

For DTC to run, the following conditions must be met:

• DTCs P0101-P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0130-P0135, P0137, P0138, P0140, P0141, P0150-P0155, P0171, P0172, P0174, P0175, P0201-P0206, P0300, P0325, P0336, P0341, P0401, P0403-P0405, P0440, P0442, P0443, P0446, P0449, P0502, P0503, P0506, P0507, P1120, P1125, P1133, P1134, P1153, P1154, P1220, P1221, P1336, P1352, P1361, P1362, P1441, or P1523 are not set.
• Engine has been running longer than 10 minutes.
• Engine Coolant Temperature (ECT) is more than 158°F (70°C), and less than 255°F (124°C).
• Barometric Pressure (BARO) is more than 75 kPa.
• Vehicle is in closed loop.
• Intake Air Temperature (IAT) is more than -4°F (-20°C), and less than 212°F (100°C).
• Battery voltage more than 10.7 volts.
• Warm the catalyst
  
  Fully open hood. Place transmission in Park (automatic transmission), or Neutral (manual transmission). Set parking brake. Press and hold brake pedal. Each time engine is started, diagnostic can run up to 18 times. After 10 minute run time, and before diagnostic runs first time, engine must run an additional 5 minutes at 1500-2000 RPM. For any additional tests on same key cycle, RPM must be 1500-2000 RPM for 1 minute. To activate diagnostic, return engine to idle and put vehicle in Drive or depress clutch.
• Test the catalyst
  
  Place transmission in Drive (automatic transmission), or Neutral and depress clutch (manual transmission). Within 60 seconds, air/fuel ratio will go rich (below 14.0) for up to 5 seconds, then air/fuel ratio may go lean (above 15.3) for up to 8 seconds. Use scan tool to check if DTC P0420 has passed or failed this key cycle.

DTC will set when PCM determines catalyst's oxygen storage capacity is less than an acceptable threshold.