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TROUBLESHOOTING MULTIPORT FUEL INJECTION (MPI) 13A-183 Code No. P0431: Warm Up Catalyst Malfunction (Cylinder 2, 3) FUNCTION • The signal from the cylinder 2, 3 oxygen sensor (rear) differs from the cylinder 2, 3 oxygen sensor • The engine-ECU <M/T> or engine-A/T-ECU <A/T> compares the output of the cylinder 2, 3 TROUBLE JUDGMENT Check Conditions • Engine speed is 3,000 r/min or lower. • The accelerator pedal is open. • Air flow sensor output is 8 gm/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. • For 10 seconds per cycle, the engine-ECU <M/T> engine-A/T-ECU <A/T> monitors 7 cycles • Short-term fuel trim is between −25 % or higher and +25 % or lower. • The cumulative air flow sensor output is 2,931 g or higher. Judgment Criterion • The cylinder 2, 3 oxygen sensor (rear) signal frequency divided by cylinder 2, 3 oxygen sensor PROBABLE CAUSE • Catalytic converter deteriorated • Failed cylinder 2, 3 oxygen sensor (front) • Failed cylinder 2, 3 oxygen sensor (rear) • Failed engine-ECU <M/T> • Failed engine-A/T-ECU <A/T> DIAGNOSIS PROCEDURE STEP 1. Check for leakage of exhaust emission Q: Is the check result normal? YES : Go to Step 2 . NO : Repair. STEP 2. MUT-III data list • Refer to Data List Reference Table a. Item 39: Cylinder 2, 3 oxygen sensor (front) Q: Are the check results normal? YES : Go to Step 3 . NO : Perform the diagnosis code classified check STEP 3. MUT-III data list • Item 39: Cylinder 2, 3 oxygen sensor (front) OK: 0 − 0.4 and 0.6 − 1.0 volt should alternate 15 times or more within 10 seconds (engine Q: Is the check result normal? YES : Go to Step 4 . NO : Replace the cylinder 2, 3 oxygen sensor STEP 4. Replace the cylinder 2, 3 oxygen sensor • After replacing the cylinder 2, 3 oxygen sensor (rear), re-check the trouble symptoms. Q: Is the check result normal? YES : Check end. NO : Go to Step 5 . STEP 5. Replace the catalytic converter (cylinder • After replacing the catalytic converter (cylinder 2, 3), re-check the trouble symptoms. Q: Is the check result normal? YES : Replacing engine-ECU <M/T> or engine-A/T-ECU <A/T>. NO : Check end. |