P0421
DTC P0421: Warm up catalyst Efficiency Below Threshold (bank 1)TECHNICAL 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 PCM compares the output of the front and rear heated oxygen sensor signals.
DESCRIPTIONS OF MONITOR METHODS
Front and rear heated 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.
- Oxygen sensor heater (front).
- Oxygen sensor heater (rear).
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:
Logic Flow Chart
Check Conditions
- Engine speed is lower than 3,000 r/min.
- Accelerator pedal is open.
- Mass airflow is between 9 and 30 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 PCM monitors for this condition for 7 cycles of 12 seconds each during the drive cycle.
- Short-term fuel trim is higher than -30 percent and lower than +25 percent.
- The cumulative mass airflow is higher than 1,638 g.
Judgment Criteria
- When the monitoring for 12 seconds is carried out 7 times, the frequency ratio of rear and front is 0.8 or more.
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:)
- Right bank side catalytic converter deteriorated.
- Right bank heated oxygen sensor failed.
- Exhaust leak.
- PCM failed.
DIAGNOSIS
Required Special Tools:
- MB991958: Scan tool (MUT-III Sub Assembly)
- MB991824: V.C.I
- MB991827: USB Cable
- MB991910: Main Harness A
STEP 1. Check for exhaust leak.
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 69: Heated Oxygen Sensor Bank 1, Sensor 2 (right 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 69, Heated Oxygen Sensor Bank 1, Sensor 2 (right rear).
- Warming up the engine When the engine is revved, the output voltage should repeat 0 volt and 0.6 to 10 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 (Bank 1, Sensor 2), DTC P0137 - Heated Oxygen Sensor Circuit Low Voltage (Bank 1, Sensor 2), DTC P0138 - Heated Oxygen Sensor Circuit High Voltage (Bank 1, Sensor 2), DTC P0139 - Heated Oxygen Sensor Circuit Slow Response (Bank 1, Sensor 2).
STEP 3. Using scan tool MB991958, check data list item 39: Heated Oxygen Sensor Bank 1, Sensor 1 (right front).
1. Start the engine and run at idle.
2. Set scan tool MB991958 to the data reading mode for item 39, Heated Oxygen Sensor Bank 1, Sensor 1 (right 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 (Bank 1, Sensor 1), DTC P0131 - Heated Oxygen Sensor Circuit Low Voltage (Bank 1, Sensor 1), DTC P0132 - Heated Oxygen Sensor Circuit High Voltage (Bank 1, Sensor 1), DTC P0133 - Heated Oxygen Sensor Circuit Slow Response (Bank 1, Sensor 1), DTC P0134 - Heated Oxygen Sensor Circuit No Activity Detected (Bank 1, Sensor 1).
STEP 4. Using scan tool MB991958, check data list item 39: Heated Oxygen Sensor Bank 1, Sensor 1 (right front).
1. Start the engine and run at idle.
2. Set scan tool MB991958 to the data reading mode for item 39, Heated Oxygen Sensor Bank 1, Sensor 1. (right 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 right bank 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. Read the diagnostic trouble code.
Q: Is DTC P0421 set?
YES: Replace the right bank side 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. Read the diagnostic trouble code.
Q: Is DTC P0421 set?
YES: Replace the 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.