Code No. P0420: Catalyst malfunction
FUNCTION
- The signal from the heated oxygen sensor (rear) differs
from the heated oxygen sensor (front). That is because the catalytic converter purifies exhaust
gas. When the catalytic converter has deteriorated, the signal from the heated oxygen sensor
(front) becomes similar to the heated oxygen sensor (rear).
- The engine-ECU compares the output of the front and rear heated oxygen sensor signals.
TROUBLE JUDGMENT
Check Conditions
- Engine speed is less than 3,500 r/min <M/T>.
- Engine speed is less than 3,000 r/min <CVT>.
- Accelerator pedal is open.
- Air flow sensor output is more than 6.4 g/sec and less than 65 g/sec.
- More than 3 seconds have elapsed after the above mentioned three conditions have
been met.
- Intake air temperature is more than -10°C.
- Barometric pressure is more than 76 kPa.
- Under the closed loop air/fuel ratio control.
- Vehicle speed is more than 1.5 km/h.
- The engine-ECU monitors for this condition for 5 cycles of 10 seconds each during
the drive cycle.
- Short-term fuel trim is more than -25 % and less than +25 %.
- The cumulative air flow is more than 1,638 g.
- When the monitoring for 10 seconds is carried out 5 times, the frequency ratio of
oxygen sensor (rear) and oxygen sensor (front) is more than 0.7.
PROBABLE CAUSE
- Catalytic converter deteriorated
- Failed oxygen sensor (front)
- Failed 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?
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Go to Step 2 . |
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Repair. |
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STEP 2. M.U.T.-III data list |
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Q.
Is the check result normal?
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Go to Step 3 . |
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Perform the diagnosis code classified check procedure for the sensor that has
shown an abnormal data valve (Refer to Inspection Chart for Diagnosis Codes ). |
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STEP 3. M.U.T.-III data list |
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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?
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Go to Step 4 . |
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Replace the oxygen sensor (front). |
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STEP 4. Replace the oxygen sensor (rear). |
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Q.
Is the check result normal?
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Check end. |
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Go to Step 5 . |
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STEP 5. Replace the catalytic converter. |
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Q.
Is the check result normal?
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Replace the engine-ECU. |
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Check end. |
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