Inspection Procedure

HINT:

Read freeze frame data using the hand held tester or the OBD II scan tool. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.

1. READ OUTPUT DTC (IN ADDITION - P0420) 
   1. Read the DTCs with the OBD II scan tool or the hand held tester.

      Result: 

      RESULT CHART
      
      

      Display	Proceed to
      Only DTC P0420 is output.	A
      P0420 and other DTCs are output.	B

   HINT:

   If any other cord besides P0420 are output, perform the troubleshooting for those DTCs first.

   1. B: GO TO RELEVANT DTC CHART (See  DIAGNOSTIC TROUBLE CODE CHART  ) 
   2. A Go to next step. 
2. CHECK FOR EXHAUST GAS LEAKAGE 

   OK: No gas leakage. 

   1. NG: REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT 
   2. OK: Go to next step. 
3. CHECK AIR FUEL RATIO SENSOR (BANK 1 SENSOR 1) (See ) 
   1. NG: REPAIR OR REPLACE AIR FUEL RATIO SENSOR 
   2. OK: Go to next step. 
4. CHECK HEATED OXYGEN SENSOR (BANK 1 SENSOR 2) (See  DTC P0136 OXYGEN SENSOR CIRCUIT MALFUNCTION (BANK 1 SENSOR 2), DTC P0137: OXYGEN SENSOR CIRCUIT LOW VOLTAGE (BANK 1 SENSOR 2), DTC P0138: OXYGEN SENSOR CIRCUIT HIGH VOLTAGE (BANK 1 SENSOR 2)  ) 

   OK: During air-fuel ratio feedback, the O2S's output alternates between rich and lean. 

   1. NG: REPAIR OR REPLACE HEATED OXYGEN SENSOR 
   2. OK: REPLACE THREE-WAY CATALYTIC CONVERTER (BOTH FRONT, REAR CATALYSTS) 

   HINT:

   The ECM monitors the front catalyst to judge the degree of deterioration in both the front and rear catalysts. Therefore, both the catalysts must be replaced together when this DTC is set.