P0420 – Catalyst Malfunction MMC Colt



FUNCTION

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

  • TROUBLE JUDGMENT

  • Engine speed is 3,000 r/min or lower.
  • Depress the accelerator pedal.
  • Mass air flow rate output is 8 gm/s or higher.
  • 3 seconds or more elapsed after the above mentioned 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 monitors 7 cycles of this condition during the drive cycle.
  • Short-term fuel trim is between -25% or higher and +25% or lower.
  • The cumulative manifold absolute pressure sensor output is 2,931 g or higher.
  • The oxygen sensor (rear) signal frequency divided by oxygen sensor (front) signal frequency is 0.8 or more.

  • PROBABLE CAUSES

  • 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?

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

  • Item No. 9: Oxygen sensor (front)
  • Item No. 10: Oxygen sensor (rear)
  • Q. Are the check result normal?

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

  • Item No. 9: Oxygen sensor (front)
  • Q. Is the check result normal?

    STEP 4. Replace the oxygen sensor (rear).

  • After replacing the oxygen sensor (rear), re-check the trouble symptoms.
  • Q. Is the check result normal?

    STEP 5. Replace the catalytic converter.

  • After replacing the catalytic converter, re-check the trouble symptoms.
  • Q. Is the diagnosis code set?

    Author: admin