P0420

DTC P0420: Warm Up Catalyst Efficiency Below Threshold

TECHNICAL DESCRIPTION

- The signal from the heated oxygen sensor (rear) differs from the linear air-fuel ratio sensor, because the catalytic converter purifies exhaust gas.
When the catalytic converter has deteriorated, the signal from the linear air-fuel ratio sensor becomes similar to the heated oxygen sensor (rear).

- The ECM compares the output of the linear air-fuel ratio sensor and heated oxygen sensor (rear) signals.

DESCRIPTIONS OF MONITOR METHODS

Linear air-fuel ratio sensor and heated oxygen sensor
(rear) rich/lean switching frequencies are nearly equal.

MONITOR EXECUTION

Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

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

- Linear air-fuel ratio sensor monitor

- Heated oxygen sensor (rear) monitor

- Linear air-fuel ratio sensor heater monitor

- Heated oxygen sensor (rear) heater monitor

- Heated oxygen sensor offset voltage monitor

- Misfire monitor

- Fuel system monitor

- Heated oxygen sensor (rear) feedback control system
Sensor (The sensor below is determined to be normal)

- Mass airflow sensor

- Engine coolant temperature sensor

- Intake air temperature sensor

- Barometric pressure sensor

- Throttle position sensor

- Accelerator pedal position sensor

DTC SET CONDITIONS

Logic Flow Chart






Check Conditions

- Engine speed is lower than 3,000 r/min.

- Accelerator pedal is depressed.

- Mass airflow is between 10 and 45 g/sec.

- More than 3 seconds have elapsed after the above-mentioned three conditions have been met.

- Intake air temperature is higher than -10°C (14°F).

- Barometric pressure is higher than 76 kPa (22.4 in.Hg).

- Under the closed loop air/fuel ratio control.

- Vehicle speed is 1.5 km/h (1.0 mph) or more.

- The ECM monitors the maximum 3 times per drive cycle under these conditions.

- Short-term fuel trim is higher than -25 percent and lower than +25 percent.

- The cumulative mass airflow is higher than 1,741 g.

- The linear air-fuel ratio sensor rich/lean switching frequency is more than 8 times.
Judgement Criterion

- When the monitoring for 10 seconds is carried out 5 times, the frequency ratio of heated oxygen sensor (rear) and linear air-fuel ratio sensor signals is the specified value or more.
NOTE:
The specified value varies depending on the average air flow rate.

OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 4 OBD- II Drive Cycle.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)

- Catalytic converter deteriorated.

- ECM failed.

DIAGNOSIS

STEP 1. Replace the catalytic converter.

(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 4 OBD- II Drive Cycle.

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

Q. Is DTC P0420 set?

YES Replace the ECM. When the ECM is replaced, register the ID code. Refer to ID registration procedure manual - ID codes registration judgement table [Vehicles with KOS] or ID registration procedure manual - ID codes registration judgement table [Vehicles with WCM].
NO The inspection is complete.