P0421
P0421: Warmup Catalyst Efficiency Below Threshold - bank 1 (California)
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.
DTC SET CONDITIONS
Check Area
- Engine speed is lower than 3,000 r/min.
- Volume air flow sensor output frequency is between 69 and 156 Hz <3.0L Engine> or 69 and 169 Hz <3.5L Engine>.
- Intake air temperature is higher than -10° C (14° F).
- Barometric pressure is higher than 76 kPa (11 psi).
- Closed throttle position switch: "OFF" <3.0L Engine>
- Throttle valve is opened (not fully closed) <3.5L Engine>
- In closed loop.
- Vehicle speed is 1.5 km/h (0.93 mph) or more.
- Monitoring time: 84 seconds.
Judgment Criteria
- The right bank heated oxygen sensor (rear) signal and right bank heated oxygen sensor (front) signal are similar.
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.
- PCM failed.
DIAGNOSIS
Required Special Tool:
MB991502: Scan Tool (MUT-II)
STEP 1. Check the exhaust leakage.
1. Are there any cracks, etc., in the exhaust manifold or front exhaust pipe?
If no, go to Step 2.
If yes, repair or replace. Then go to Step 7.
CAUTION: To prevent damage to the scan tool, turn the ignition switch "OFF" before connecting or disconnecting the scan tool.
STEP 2. Using scan tool MB991502, check data list item 59: Heated Oxygen Sensor (rear).
1. Run in L range at wide open throttle.
- The output voltage should be between 0.6 and 1.0 volt after the engine is warmed.
If within specifications, go to Step 3.
If not within specifications, refer to DTC P0136 - O2 Sensor Circuit Malfunction (bank 1 sensor 2)
CAUTION: To prevent damage to the scan tool, turn the ignition switch "OFF" before connecting or disconnecting the scan tool.
STEP 3. Using scan tool MB991502, check data list item 11: Heated Oxygen Sensor (front)
- The output voltage should be between 0.6 and 1.0 volt after racing the engine.
If within specifications, go to Step 4.
If not within specifications, refer to DTC P0130 - O2 Sensor Circuit Malfunction (bank 1 sensor 1)
CAUTION: To prevent damage to the scan tool, turn the ignition switch "OFF" before connecting or disconnecting the scan tool.
STEP 4. Using scan tool MB991502, check data list item 11: Heated Oxygen Sensor (front).
1. 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.
If within specifications, go to Step 5.
If not within specifications, 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 Procedure 3 - Catalytic Converter Monitor.
2. Read the diagnostic trouble code (DTC).
If DTC P0421 is output, replace the right bank side catalytic converter. Then go to Step 6.
If DTC P0421 is not output, 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 Procedure 3 - Catalytic Converter Monitor.
2. Read the diagnostic trouble code (DTC).
If DTC P0421 is output, replace the PCM. Then go to Step 7.
If DTC P0421 is not output, 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 Procedure 3 - Catalytic Converter Monitor.
2. Read the diagnostic trouble code, and confirm that a diagnostic trouble code is not being output.