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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 379 (Engine Controls Self-Diagnostics - 3.4L) >> Diagnostic Tests >> DTC P0420: TWC System - Low Efficiency >> Conditions For Running

Conditions For Running

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  1. Meet the conditions for engine warm-up. Use the scan tool catalyst data list to verify the following conditions:
    • DTCs P0030, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0171, P0172, P0201-P0206, P0300, P0336, P0341, P0404, P0405, P0440, P0442, P0443, P0502, P0503, P0506, P0507, P1133, P1134, P1351, P1352, P1361, P1362 or P1441 are not set.
    • The engine has been running longer than 10 minutes.
    • The Engine Coolant Temperature (ECT) sensor parameter is 169-255°F (76-124°C).
    • The Barometric Pressure (BARO) is above 75 kPa.
    • The vehicle is in Closed Loop.
    • The Intake Air Temperature (IAT) is -4 to 212°F (-20 to 100°C).
    • The battery voltage more than 10.7 volts.
  2. Warm up the catalyst:
    • Fully open the hood.
    • The vehicle is in Drive (A/T) or in Neutral (M/T).
    • Set the parking brake.
    • Press and hold the service brake.
    • Each time the engine is started the diagnostic can run up to 18 times. After the 10 minute run time, and before the diagnostic runs the first time, the engine must run an additional 5 minutes between 1500-2500 RPM. For any additional tests on the same key cycle, the engine must be between 1500-2500 RPM for one minute.
    • In order to activate the diagnostic, return the engine to idle and place the vehicle in drive, or depress the clutch pedal for a manual transmission.
  3. Check the catalyst.
    • The transaxle is in Drive, for automatic transaxles, or Neutral for manual transaxles with the clutch pedal depressed.
    • Within 60 seconds the air/fuel ratio will go lean, below 14.1, for up to 7 seconds. The air/fuel ratio may then go rich, above 15.3, for up to 7 seconds.
    • Verify if DTC P0420 has passed or failed this key cycle using a scan tool.
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