P0421
DTC P0421: Warm Up Catalyst Efficiency Below ThresholdTECHNICAL DESCRIPTION
- The signal from the rear heated oxygen sensor differs from the front heated oxygen sensor. That is because the catalytic converter purifies exhaust gas. When the catalytic converter has deteriorated, the signal from the front heated oxygen sensor becomes similar to the rear heated oxygen sensor.
- The ECM
DESCRIPTIONS OF MONITOR METHODS
Front and rear oxygen sensor 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)
- Heated oxygen sensor (front) monitor
- Heated oxygen sensor (rear) monitor
- Heated oxygen sensor heater (front) monitor
- Heated oxygen sensor heater (rear) monitor
- Misfire monitor
- Fuel system monitor
- Air/fuel ratio feedback monitor
Sensor (The sensor below is determined to be normal)
- Volume airflow sensor
- Engine coolant temperature sensor
- Intake air temperature sensor
- Barometric pressure sensor
- Throttle position sensor
DTC SET CONDITIONS
Logic Flow Chart:
Logic Flow Chart
Check Conditions
- Engine speed is lower than 3,000 r/min.
- Volume airflow sensor output frequency is at between 63 and 169 Hz.
- The throttle valve is open.
- More than 3 seconds has elapsed after the three above-mentioned 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 mph) or more.
- The ECM
- Short-term fuel trim is at between -25 and +25 percent.
- The cumulative volume airflow sensor output frequency is higher than 4,000 Hz.
Judgement Criteria
- The frequency ratio of heated oxygen sensor (rear) and heated oxygen sensor (front) is more than 0.8.
OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 3 - Catalytic Converter Monitor. OBD-II Drive Cycle Pattern Lists
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Catalytic converter deteriorated.
- Heated oxygen sensor failed.
- ECM failed.
- PCM failed.
DIAGNOSIS
Required Special Tools:
- MB991958 (MUT-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991911: Main Harness B
STEP 1. Check the exhaust leaks.
Q: Are there any abnormalities?
YES: Repair it. Then go to Step 7.
NO: Go to Step 2.
STEP 2. Using scan tool MB991958, check data list item 59: Heated Oxygen Sensor (rear).
CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
1. Connect scan tool MB991958 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991958 to the data reading mode for item 59, Heated Oxygen Sensor (rear).
- Warming up the engine. When the engine is revved, the output voltage should repeat 0 volt and 0.6 to 1.0 volt alternately.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: Go to Step 3.
NO: Refer to DTC P0136 - Heated Oxygen Sensor Circuit (sensor 2), DTC P0137 - Heated Oxygen Sensor Circuit Low Voltage (sensor 2), DTC P0138 - Heated Oxygen Sensor Circuit High Voltage (sensor 2), DTC P0139 - Heated Oxygen Sensor Circuit Slow Response (sensor 2).
STEP 3. Using scan tool MB991958, check data list item 11: Heated Oxygen Sensor (front).
1. Start the engine and run at idle.
2. Set scan tool MB991958 to the data reading mode for item 11, Heated Oxygen Sensor (front).
- Warming up the engine. When the engine is revved, the output voltage should be 0.6 to 1.0 volt.
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: Go to Step 4.
NO: Refer to DTC P0130 - Heated Oxygen Sensor Circuit (sensor 1), DTC P0131 - Heated Oxygen Sensor Circuit Low Voltage (sensor 1), DTC P0132 - Heated Oxygen Sensor Circuit High Voltage (sensor 1), DTC P0133 - Heated Oxygen Sensor Circuit Slow Response (sensor 1), DTC P0134 - Heated Oxygen Sensor Circuit No Activity Detected (sensor 1).
STEP 4. Using scan tool MB991958, check data list item 11: Heated Oxygen Sensor (front).
1. Start the engine and run at idle.
2. Set scan tool MB991958 to the data reading mode for item 11, Heated Oxygen Sensor (front).
3. Keep the engine speed at 2,000 r/min.
- 0 - 0.4 and 0.6 - 1.0 volt should alternate 15 times or more within 10 seconds.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: Go to Step 5.
NO: Replace the heated oxygen sensor (front). Then go to Step 7.
STEP 5. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 3 - Catalytic Converter Monitor. OBD-II Drive Cycle Pattern Lists
2. Check the diagnostic trouble code (DTC).
Q: Is DTC P0421 set?
YES: Replace the catalytic converter. Then go to Step 6.
NO: The inspection is complete.
STEP 6. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 3 - Catalytic Converter Monitor. OBD-II Drive Cycle Pattern Lists
2. Check the diagnostic trouble code (DTC).
Q: Is DTC P0421 set?
YES: Replace the ECM or PCM. Then go to Step 7.
NO: The inspection is complete.
STEP 7. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 3 - Catalytic Converter Monitor. OBD-II Drive Cycle Pattern Lists
2. Check the diagnostic trouble code (DTC).
Q: Is DTC P0421 set?
YES: Retry the troubleshooting.
NO: The inspection is complete.