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Test Procedure

  1. HF1 DIAGNOSTIC TROUBLE CODE (DTC) P0420: CHECK FOR MISFIRE DETECTION MONITOR DTCS 
    NOTE: Internal deterioration of a catalytic converter is usually caused by abnormal engine operation upstream of the catalyst. Events that can produce higher than normal temperatures in the catalyst are particularly suspect. For example, misfiring can cause higher than normal catalyst operating temperatures.
    NOTE: Make sure the customer has not noticed a high engine oil consumption. An engine that consumes oil at a high rate deposits high levels of phosphorus on the catalyst and reduces the catalyst efficiency.
    • Carry out the PCM self-test.

    Are DTCs P0300, P0301, P0302, P0303 or P0304 present? 

    Yes No
    DISREGARD the DTC P0420 at this time. GO to DIAGNOSTIC TROUBLE CODE (DTC) CHARTS AND DESCRIPTIONS for pinpoint test direction and REPAIR the misfire DTCs. GO to  HF2.
  2. HF2 CHECK FOR HEATED OXYGEN SENSOR (HO2S) DTCS 
    NOTE: Incorrect HO2S signal input can cause an abnormal temperature in the catalyst.
    • Carry out the PCM self-test.

    Are DTCs P0030, P0053, P0054, P0130, P0133, P0134, P0135, P0138, P0141, P1127, P2096, P2097, P2195, P2196, P2270 or P2271 present? 

    Yes No
    DISREGARD the DTC P0420 at this time. GO to DIAGNOSTIC TROUBLE CODE (DTC) CHARTS AND DESCRIPTIONS for pinpoint test direction and REPAIR the HO2S DTCs. GO to  HF3.
  3. HF3 CHECK FOR CYLINDER HEAD TEMPERATURE (CHT) SENSOR DTCS 
    NOTE: CHT sensor DTCs can indicate the thermostat is not operating correctly or the engine coolant level is not filled to specification, producing above normal operation temperatures.
    • Carry out the PCM self-test.

    Are DTCs P0116, P0119, P0128, P1285, P1288, P1289, P1290 or P1299 present? 

    Yes No
    DISREGARD the DTC P0420 at this time. GO to DIAGNOSTIC TROUBLE CODE (DTC) CHARTS AND DESCRIPTIONS for pinpoint test direction and REPAIR the CHT DTCs. GO to  HF4.
  4. HF4 CHECK FOR ANY OTHER DTCS 

    Are there any other DTCs recorded in HF1 (not including the initial P0420)? 

    Yes No
    DISREGARD the current diagnostic trouble code (DTC) at this time. DIAGNOSE the next DTC. GO to DIAGNOSTIC TROUBLE CODE (DTC) CHARTS AND DESCRIPTIONS . GO to  HF5.
  5. HF5 CHECK THE FUEL PRESSURE 
    WARNING: THE FUEL SYSTEM REMAINS PRESSURIZED WHEN THE ENGINE IS NOT RUNNING. TO PREVENT INJURY OR FIRE, USE CAUTION WHEN WORKING ON THE FUEL SYSTEM. REFER TO THE FUEL SYSTEM WARNING INFORMATION AT THE BEGINNING OF Pinpoint Test HC  . FAILURE TO FOLLOW THESE INSTRUCTIONS MAY RESULT IN PERSONAL INJURY.

    Is the ignition ON, engine OFF fuel system pressure between 262 - 448 kPa (38 - 65 psi)? 

    Yes No
    GO to  HF6. GO to PINPOINT TEST HC .
  6. HF6 CHECK FOR LEAKS IN THE EXHAUST SYSTEM 
    NOTE: If a catalyst is in series with a leaking exhaust system, it can fail the catalyst efficiency monitor test.
    • Inspect the exhaust system for leaks, cracks, loose connections, punctures, or non-factory modifications.

    Is a concern present? 

    Yes No
    REPAIR as necessary.
    Clear the PCM DTCs. REPEAT the self-test.    		 GO to  HF7.
  7. HF7 CHECK FOR RESTRICTIONS IN THE EXHAUST SYSTEM 
    NOTE: A slight pressure in the exhaust system is normal, but excessive exhaust back pressure seriously affects engine operation.
    • Inspect the following for damage or restrictions:
      • front and rear exhaust pipes
      • catalytic converter
      • muffler and tailpipe assembly

    Is a concern present? 

    Yes No
    REPAIR as necessary.
    Clear the PCM DTCs. REPEAT the self-test.    		 GO to  HF8.
  8. HF8 CHECK FOR EXCESSIVE EXHAUST BACK PRESSURE 
    • The internal condition of exhaust system and its ability to flow can be checked with an exhaust back pressure tool.

    Is an exhaust back pressure tester available? 

    Yes No
    GO to  HF9. GO to  HF10.
  9. HF9 CHECK FOR EXCESSIVE EXHAUST BACK PRESSURE WITH EXHAUST BACK PRESSURE TOOL 
    NOTE: Typical exhaust back pressure, when measured near the exhaust manifold and at normal engine operating temperature, should not exceed 20.7 kPa (3 psi) at idle and 55.2 kPa (8 psi) at wide open throttle (WOT) under load.
    • Install an exhaust back pressure tester and follow the tool manufacturer installation and testing instructions.

    Does the exhaust back pressure test indicate a restriction? 

    Yes No
    REPAIR as necessary. Clear the PCM DTCs. REPEAT the self-test.
    To continue diagnosis of a symptom (lack of power, loss of power, or no start), REFER to SYMPTOM CHARTS .    		 No indication of restrictions or leaks has been detected in the exhaust system. Clear the PCM DTCs. REPEAT the self-test.
    To continue diagnosis of a symptom (lack of power, loss of power, or no start), REFER to SYMPTOM CHARTS .
  10. HF10 CARRY OUT THE CATALYST MONITOR DRIVE CYCLE 

    Is DTC P0420 present? 

    Yes No
    INSTALL a new catalyst between the monitored HO2Ss. Do not install a new unmonitored catalyst unless it is repaired as an assembly. The test is complete and no concerns are present.
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