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DTC P0421-00: Catalytic converter monitor
 
 
 
 
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 set 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
  • Fuel tank pressure sensor
 
 
DTC SET CONDITIONS
Logic Flow Chart
Check Conditions
  • Engine speed is 3,500 r/min or lower.
  • Mass airflow sensor output is between 13 and 50 g/sec (between 0.46 and 1.76 oz./sec).
  • More than 3 seconds have elapsed after the above mentioned two conditions have been met.
  • Under the closed loop air-fuel ratio control.
  • Barometric pressure is higher than 76 kPa (22.4 in.Hg).
  • Engine coolant temperature is higher than 65°C (149°F).
  • Intake air temperature is higher than –10°C (14°F).
  • Vehicle speed is higher than 1.5 km/h (1.0 mph).
  • 5 seconds or more have passed since the estimated catalytic converter temperature is higher than 600°C (1,112°F).
  • Short-term fuel trim is higher than –25 percent and lower than +25 percent.
  • The linear air-fuel ratio sensor rich/lean switching frequency is more than 8 times.
Judgment 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.
    • Monitoring stops when the estimated catalytic converter temperature is 500°C (932°F) or lower.
 
 
FAIL-SAFE AND BACKUP FUNCTION
None.
 
 
OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function, OBD-II Drive Cycle – Pattern 5 OBD- II DRIVE CYCLE.
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
  • Catalyst (built into the main catalytic converter assembly) deteriorated.
  • ECM failed.
 
 
DIAGNOSIS
Required Special Tools:
  • MB992744: Vehicle communication interface-Lite (V.C.I.-Lite)
  • MB992745: V.C.I.-Lite main harness A
  • MB992747: V.C.I.-Lite USB cable short
  • MB992748: V.C.I.-Lite USB cable long
1.STEP 1. Test the OBD-II drive cycle after replacing the main catalytic converter assembly.
After replacing the main catalytic converter assembly and erasing the DTC, carry out test drive with the drive cycle pattern, and recheck the DTC.
(1) Replace the main catalytic converter assembly (Refer to ENGINE, Engine, Motor and Emission Control – Emission Control – Exhaust Gas Purification System CATALYTIC CONVERTER REMOVAL AND INSTALLATION).
(2) Use scan tool (M.U.T.-III SE) to erase the DTC.
(3) Carry out test drive with the drive cycle pattern (Refer to Diagnostic Function, OBD-II Drive Cycle – Pattern 5 OBD- II DRIVE CYCLE).
(4) Use scan tool (M.U.T.-III SE) to recheck the DTC.
Q: Is DTC P0421-00 set?
Replace the ECM (Refer to ENGINE CONTROL MODULE (ECM) REMOVAL AND INSTALLATION).
The inspection is complete.