Code No. P0420: Catalyst malfunction

FUNCTION

• The signal from the heated oxygen sensor (rear) differs from the heated oxygen sensor (front). That is because the catalytic converter purifies exhaust gas. When the catalytic converter has deteriorated, the signal from the heated oxygen sensor (front) becomes similar to the heated oxygen sensor (rear).
  
• The engine-ECU compares the output of the front and rear heated oxygen sensor signals.
  

TROUBLE JUDGMENT

• Engine speed is less than 3,500 r/min <M/T>.
  
• Engine speed is less than 3,000 r/min <CVT>.
  
• Accelerator pedal is open.
  
• Air flow sensor output is more than 6.4 g/sec and less than 65 g/sec.
  
• More than 3 seconds have elapsed after the above mentioned three conditions have been met.
  
• Intake air temperature is more than -10°C.
  
• Barometric pressure is more than 76 kPa.
  
• Under the closed loop air/fuel ratio control.
  
• Vehicle speed is more than 1.5 km/h.
  
• The engine-ECU monitors for this condition for 5 cycles of 10 seconds each during the drive cycle.
  
• Short-term fuel trim is more than -25 % and less than +25 %.
  
• The cumulative air flow is more than 1,638 g.
  

• When the monitoring for 10 seconds is carried out 5 times, the frequency ratio of oxygen sensor (rear) and oxygen sensor (front) is more than 0.7.
  

PROBABLE CAUSE

• Catalytic converter deteriorated
  
• Failed oxygen sensor (front)
  
• Failed oxygen sensor (rear)
  
• Failed engine-ECU
  

	Go to Step 2 .

	Repair.

	Go to Step 3 .

	Perform the diagnosis code classified check procedure for the sensor that has shown an abnormal data valve (Refer to Inspection Chart for Diagnosis Codes ).

	Go to Step 4 .

	Replace the oxygen sensor (front).

	Check end.

	Go to Step 5 .

	Replace the engine-ECU.

	Check end.