Inspection Procedure

HINT:

Read freeze frame data using the intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air-fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.

1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0420) 
   1. Connect the intelligent tester to the DLC3.
   2. Turn the ignition switch to the ON position and turn the tester on.
   3. Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DTC INFO / CURRENT CODES.
   4. Read the DTCs.

      Result 

      DTC RESULT REFERENCE
      
      

      Display (DTC Output)	Proceed to
      P0420	A
      P0420 and other DTCs	B

      HINT:

      If any DTCs other than P0420 are output, troubleshoot those DTCs first.

   B: GO TO  DTC CHART  

   A: GO TO NEXT STEP 

2. PERFORM ACTIVE TEST BY INTELLIGENT TESTER (A/F CONTROL) 
   1. Connect the intelligent tester to the DLC3.
   2. Start the engine and turn the tester on.
   3. Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.
   4. On the tester, select the following menu items: DIAGNOSIS/ ENHANCED OBD II /ACTIVE TEST/A/F CONTROL.
   5. Perform the A/F CONTROL operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).
   6. Monitor the voltage outputs of the A/F and HO2 sensors (AFS B1S1 and O2S B1S2) displayed on the tester.

      HINT:

      • The A/F CONTROL operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
      • Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

      Standard voltage 

      DATA LIST
      
      

      Tester Display (Sensor)	Injection Volume	Status	Voltage
      AFS B1S1 (A/F)	+25%	Rich	Less than 3.0
      AFS B1S1 (A/F)	-12.5%	Lean	More than 3.35
      O2S B1S2 (HO2)	+25%	Rich	More than 0.55
      O2S B1S2 (HO2)	-12.5%	Lean	Less than 0.4

      Result 

      RESULT REFERENCE
      
      

      Status AFS B1S1	Status O2S B1S2	A/F Condition and A/F Sensor Condition	Misfire	Suspected Trouble Area	Proceed to
      Lean/Rich	Lean/Rich	Normal	-	Three-Way Catalytic Converter (TWC) Gas leakage from exhaust system	A
      Lean	Lean/Rich	A/F sensor malfunction	-	A/F sensor	B
      Rich	Lean/Rich	A/F sensor malfunction	-	A/F sensor	B
      Lean/Rich	Lean	HO2 sensor malfunction	-	HO2 sensor Gas leakage from exhaust system	C
      Lean/Rich	Rich	HO2 sensor malfunction	-	HO2 sensor Gas leakage from exhaust system	C
      Lean	Lean	Actual air-fuel ratio lean	May occur	Extremely rich or lean actual air-fuel ratio Gas leakage from exhaust system	A
      Rich	Rich	Actual air-fuel ratio rich	-	Extremely rich or lean actual air-fuel ratio Gas leakage from exhaust system	A

      Lean: During A/F CONTROL, the A/F sensor output voltage (AFS) is consistently more than 3.35 V, and the HO2 sensor output voltage (O2S) is consistently less than 0.4 V.

      Rich: During A/F CONTROL, the AFS is consistently less than 3.0 V, and the O2S is consistently more than 0.55 V.

   B: CHECK AND REPLACE AIR FUEL RATIO SENSOR 

   C: CHECK AND REPLACE HEATED OXYGEN SENSOR, AND CHECK AND REPAIR EXHAUST GAS LEAKAGE 

   A: GO TO NEXT STEP 

3. INSPECT FOR EXHAUST GAS LEAK 

   OK: 

   No gas leakage. 

   NOTE: Replace both the front and rear catalysts (front exhaust pipe).

   NG: REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT 

   OK: REPLACE EXHAUST MANIFOLD CONVERTER