Catalytic Converter Monitor

This monitor applies to DTC P0421. Following conditions must be met during the test:

• Atmospheric temperature is 14°F (-10°C) or more.
• A/C switch is in OFF position.
• Selector lever is in "D" range.

Monitor takes about 20 minutes to complete. This cycle must be completed 2 times. Run monitor as shown. See Fig 1. Perform steps as follows:

1. Remove all test equipment from vehicle and install all components and connectors that were removed or disconnected during testing.
2. Start engine and accelerate to 45 MPH.
3. Travel 300 seconds or more while keeping speed at 45-60 MPH (5th gear on M/T).
4. Fully close throttle and decelerate to 35-40 MPH.
5. While keeping accelerator pedal opening degree constant (4th gear on M/T), keep speed at 35-40 MPH for 90 seconds or more (this is when monitor runs).
6. Fully close throttle and decelerate for 10 seconds. Then, quickly accelerate until speed is 35-40 MPH. Then repeat steps  4 and  5 five more times.
7. Return vehicle to shop and Turn the ignition switch to LOCK position. Recheck for DTCs. If DTC P0421 resets, go to DTC P0421: WARM UP CATALYST EFFICIENCY BELOW THRESHOLD  under DIAGNOSTIC TESTS.

Fig 1: Running Catalytic Converter Monitor

Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.