Code No. P0431: Warm Up Catalyst Malfunction (left bank)




FUNCTION



  • The signal from the left bank oxygen sensor (rear) differs from the left bank oxygen sensor (front). That is because the catalytic converter purifies exhaust gas. When the catalytic converter has deteriorated, the signal from the left bank oxygen sensor (front) becomes similar to the left bank oxygen sensor (rear).
  • The engine-ECU compares the output of the left bank oxygen sensor signals (front and rear).

TROUBLE JUDGMENT


Check Conditions
  • Engine speed is lower than 3,500 r/min.
  • Accelerator pedal is open.
  • Air flow is 5 - 60 g/sec.
  • More than 3 seconds have elapsed after the abovementioned three conditions have been met.
  • Intake air temperature is higher than -10°C.
  • Barometric pressure is higher than 76 kPa.
  • Under the closed loop air/fuel ratio control.
  • Vehicle speed is 1.5 km/h or more.
  • The engine-ECU monitors for this condition for 3 cycles of 12 seconds each during the drive cycle.
  • Short-term fuel trim is higher than -25 % and lower than +25 %.
  • The cumulative air flow is higher than 1,638 g.
Judgment Criterion
  • When the monitoring for 12 seconds is carried out 5 times, the frequency ratio of rear and front is 0.7 or more.

PROBABLE CAUSES



  • Left bank catalytic converter deteriorated
  • Failed left bank oxygen sensor (front)
  • Failed left bank oxygen sensor (rear)
  • Failed engine-ECU

DIAGNOSIS PROCEDURE


STEP 1. Check for leakage of exhaust emission from exhaust manifold.


Q. Is the check result normal?

Go to Step 2 .
Repair.

STEP 2. M.U.T.-III data list



  • Refer to Data List Reference Table .

  1. Item AE: Left bank oxygen sensor (front)
  2. Item AF: Left bank oxygen sensor (rear)

Q. Are the check results normal?

Go to Step 3 .
Perform the diagnosis code classified check procedure for the sensor that has shown an abnormal data valve (Refer to Inspection Chart for Diagnosis Code ).

STEP 3. M.U.T.-III data list



  • Item AE: Left bank oxygen sensor (front)
OK: 0 - 0.4 and 0.6 - 1.0 volt should alternate 15 times or more within 10 seconds (engine speed at 2,000 r/min).

Q. Is the check result normal?

Go to Step 4 .
Replace the left bank oxygen sensor (front).

STEP 4. Replace the left bank oxygen sensor (rear).



  • After replacing the left bank oxygen sensor (rear), re-check the trouble symptoms.

Q. Is the check result normal?

Check end.
Go to Step 5 .

STEP 5. Replace the catalytic converter (left bank).



  • After replacing the catalytic converter (left bank), re-check the trouble symptoms.

Q. Is the check result normal?

Replace the engine-ECU.
Check end.