Catalytic Converter Monitor

This monitor applies to DTCs P0420, P0421 and P0431. Following conditions must be met during the test:

• Atmospheric temperature is 14°F (-10°C) or more.
• A/C switch is in OFF position.
• If automatic transmission, selector lever is in Drive.
• If applicable, overdrive switch is in ON position.
• If applicable, power/economy changeover switch is in POWER position.

Monitor takes about 20 minutes to complete. To run monitor, use illustration. See Fig 1. Perform steps as follows:

1. Start engine.
2. Accelerate to 45 MPH.
3. Travel 300 seconds or more while keeping speed at 45-60 MPH (M/T in 5th gear on non-turbo, or 6th gear on turbo).
4. Decelerate to 35-40 MPH.
5. While keeping accelerator pedal opening degree constant, keep speed at 35-40 MPH for 90 seconds or more (M/T in 4th gear on non-turbo, or 5th gear on turbo).
6. Fully close throttle and decelerate for 10 seconds. Then, quickly accelerate until speed is 35-40 MPH. Then repeat steps 5)  and 6)  five more times.
7. Return vehicle to shop and turn ignition off.
8. Confirm DTC is not output. If DTC is output, go to appropriate DTC test in appropriate SELF-DIAGNOSTICS article.

Fig 1: Running Catalytic Converter Monitor

Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.