Code No. P0431: Warm Up Catalyst Malfunction (left bank) <Vehicles except for Brazil>

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

TROUBLE JUDGMENT

Check Conditions

Engine speed is 3,000 r/min or lower.
The accelerator pedal is open.
Air flow sensor output is 1.6 V (5 g/s) or higher.
3 seconds or more elapsed after the abovementioned conditions were satisfied.
Intake air temperature is -10°C or higher after the engine is started.
Barometric pressure is 76 kPa or higher.
Under the closed loop air/fuel ratio control.
Vehicle speed is 1.5 km/h or higher.
Short-term fuel trim is between -30 % or higher and +25 % or lower.
The cumulative air flow sensor output is 1.9 - 2.4 V (9 - 26 g/s).

Judgment Criteria

For 10 seconds per cycle, the engine-ECU <M/T> or engine-A/T-ECU <A/T> 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 0.8 or more.

PROBABLE CAUSES

Catalytic converter deteriorated
Failed left bank oxygen sensor (front)
Failed left bank oxygen sensor (rear)
Failed engine-ECU <M/T> or engine-A/T-ECU <A/T>

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 .

Item AE: Left bank oxygen sensor (front)
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 <M/T> or engine-A/T-ECU <A/T>.

	Check end.