P0431

DTC P0431: Warm Up Catalyst Efficiency Below Threshold (bank 2)

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 ECM or PCM compares the output of the front and rear heated oxygen sensor signals.

DTC SET CONDITIONS

Check Conditions
- Engine speed is lower than 3,000 r/min.
- The throttle valve is open.
- Volume airflow sensor output frequency is between 69 and 169 Hz.
- 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 (11 psi).
- Under the closed loop air/fuel ratio control.
- Vehicle speed is 1.5 km/h (0.93 mph) or more.
- The ECM or PCM monitors for this condition for 7 cycles of 12 second each during the drive cycle.
- Short-term fuel trim is higher than -30 percent and lower than +25 percent.
- The cumulative volume airflow sensor output frequency is higher than 4,000 Hz.

Judgment Criteria
- The left bank heated oxygen sensor (rear) signal frequency divided by left bank heated oxygen sensor (front) signal frequency = 0.8 or more.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Left bank side catalytic converter deteriorated.
- Left bank heated oxygen sensor failed.
- ECM failed.
- PCM failed.
- Exhaust leak

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (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 Bank 2, Sensor 2 (left 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 Bank 2, Sensor 2 (left 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 P0156 - Heated Oxygen Sensor Circuit (bank 2, sensor 2), DTC P0157 - Heated Oxygen Sensor Circuit Low Voltage (bank 2, sensor 2), DTC P0158 - Heated Oxygen Sensor Circuit High Voltage (bank 2, sensor 2), DTC P0159 - Heated Oxygen Sensor Circuit Slow Response (bank 2, sensor 2).

STEP 3. Using scan tool MB991958, check data list item 11: Heated Oxygen Sensor Bank 2, Sensor 1 (left 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 Bank 2, Sensor 1 (left 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 P0150 - Heated Oxygen Sensor Circuit (bank 2, sensor 1), DTC P0151 - Heated Oxygen Sensor Circuit Low Voltage (bank 2, sensor 1), DTC P0152 - Heated Oxygen Sensor Circuit High Voltage (bank 2, sensor 1), DTC P0153 - Heated Oxygen Sensor Circuit Slow Response (bank 2, sensor 1), DTC P0154 - Heated Oxygen Sensor No Activity Detected (bank 2, sensor 1).

STEP 4. Using scan tool MB991958, check data list item 11: Heated Oxygen Sensor Bank 2, Sensor 1 (left 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 Bank 2, Sensor 1 (left 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 left 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. Check the diagnostic trouble code (DTC).

Q: Is DTC P0431 set?

YES: Replace the left 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. Check the diagnostic trouble code (DTC).

Q: Is DTC P0431 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 P0431 set?

YES: Retry the troubleshooting.

NO: The inspection is complete.