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Home >> Infiniti >> 2004 >> Q45 >> Repair and Diagnosis >> Engine Performance >> Engine Control System >> DTC P0420, P0430: Three Way Catalyst Function >> Overall Function Check >> With GST
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With GST

  1. Start engine and warm it up to the normal operating temperature.
  2. Turn ignition switch OFF and wait at least 10 seconds.
  3. Start engine and keep the engine speed between 3,500 and 4,000 RPM for 1 minute under no load.
  4. Let engine idle for 1 minute.
  5. Set voltmeters probes between ECM terminals 114 [HO2S1 (bank 1) signal], 115 [HO2S1 (bank 2) signal] and ground, and ECM terminals 123 [HO2S2 (bank 1) signal], 124 [HO2S2 (bank 2) signal] and ground. See Figure and Figure .
  6. Keep engine speed at 2,000 RPM constant under no load.
  7. Make sure that the voltage switching frequency (high & low) between ECM terminals 123 and ground, or 124 and ground is very less than that of ECM terminals 114 and ground, or 115 and ground.

    Switching frequency ratio = A/B 

    A: Heated oxygen sensor 2 voltage switching frequency 

    B: Heated oxygen sensor 1 voltage switching frequency 

    This ratio should be less than 0.75. 

    If the ratio is greater than above, it means three way catalyst does not operate properly. Go to Diagnostic Procedure  .

NOTE: If the voltage at terminal 114 or 115 does not switch periodically more than 5 times within 10 seconds at step 5, perform trouble diagnosis for "DTC P0133, P0153" first. (See DTC P0133, P0153 HO2S1  .)
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