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-A/T-ECU compares the output of the left bank oxygen sensor signals (front and rear).

TROUBLE JUDGMENT


Check Conditions
  • 3 seconds or more elapsed after the undermentioned conditions were satisfied.

    • Engine speed is less than 3,000 r/min.
    • The accelerator pedal is open.
    • Air flow sensor output is more than 1.6 V (5g/s).
  • Intake air temperature is more than -10°C after the engine starts.
  • Barometric pressure is more than 76 kPa.
  • Under the closed loop air/fuel ratio control.
  • Vehicle speed is more than 1.5 km/h.
  • Short-term fuel trim is between -30 % and +25 %.
  • Air flow sensor output is more than 9 g/s (1.9 V) or is less than 26 g/s (2.4 V).
Judgment Criteria
  • For 10 seconds per cycle, the engine-A/T-ECU monitors 7 cycles of this condition during the drive cycle.
  • The left bank oxygen sensor (rear) signal frequency divided by left bank oxygen sensor (front) signal frequency is more than 0.8.

PROBABLE CAUSES



  • Catalytic converter deteriorated
  • Failed left bank oxygen sensor (front)
  • Failed left bank oxygen sensor (rear)
  • Failed engine-A/T-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. M.U.T.-III diagnosis code

  • Reconfirm the diagnosis code after the replacement of the left bank oxygen sensor (rear).

Q. Is the diagnosis code set?
Go to Step 5 .
Check end.

STEP 5. Replace the catalytic converter (left bank)

  • Reconfirm the diagnosis code after the replacement of the catalytic converter (left bank).

Q. Is the diagnosis code set?
Replace the engine-A/T-ECU.
Check end.