DTC P0420: Warm Up Catalyst Efficiency Below Threshold

The signal from the heated oxygen sensor (rear) differs from the heated oxygen sensor (front), 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 ECM compares the output of the heated oxygen sensor (front and rear) signals.

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)

Sensor (The sensor below is determined to be normal)

Logic Flow Chart

Check Conditions

Engine speed is less than 3,500 r/min.
Accelerator pedal is depressed.
Mass airflow rate is between 13 and 45 g/sec.
More than 3 seconds have passed after the above-mentioned three conditions have been met.
Intake air temperature is more than -10°C (14°F).
Barometric pressure is more than 76 kPa (22.4 in.Hg).
Under the closed loop air/fuel ratio control.
Vehicle speed is more than 1.5 km/h (1.0 mph).
The ECM monitors the maximum 5 times per drive cycle under these conditions.
Short-term fuel trim is between -20 percent and +17 percent.
The cumulative mass airflow is more than 1,638 g.

Judgement Criterion

When the monitoring for 10 seconds is carried out 5 times, the frequency ratio of rear and front signals is more than the specified value.

note

The specified value varies depending on the average air flow rate.

DIAGNOSIS

Required Special Tools:

(1)Replace the catalytic converter.

(2)Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 3

(3)Check the diagnostic trouble code (DTC).

	Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, Diagnosis - ID Code Registration Necessity Judgment Table <Vehicles with KOS> or GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> .

	The inspection is complete.