We don't recommend replacing your Montero's catalytic converter just yet. The question we have is what repaired did you perform to clear the oxygen sensor trouble code? If you simply reset the ECU and the check engine light has not yet turned on, this is not a great indication that a problem does not exist. There may very well be an oxygen sensor(s) which is lazy (on it's way to becoming defective soon) which triggered the check engine light. More then likely the code(s) will return after some extensive driving; subsequently, the catalyst monitor will not run if conditions are not optimum to run the CAT monitor and retrieve accurate results.
Now, if you have performed repairs, cleared the trouble codes, and are now trying to drive a Mitsubish Montero Sport drive cycle to get the monitors complete, follow the driving pattern below. Usually driving in both city and highway conditions over the course of a few days is enough to get the drive cycle to run and set the monitors. At times however, due to individual driving habits, following the recommend drive cycle is required.
Follow the drive cycle carefully. Take extra caution when performing the drive cycle on public roadways. If you feel you will be unable to follow the drive cycle safely, please seek assistance from an smog check repair station or Mitsubishi service center. They may be able to perform the drive cycle utilizing a dynamometer, and specialized scan tools. Perform the drive cycle at your own risk.
Prior to beginning the drive cycle ensure your vehicle has between 15% to 85% fuel in the gas tank, and that the engine is cold. It is best to start the driving cycle in the morning (after a cold soak).
Mitsubishi Montero Sport Drive Cycle
A. Begin from Cold Start, and ignition in OFF position for at least 1 hour. Ensure your Mitsubishi's fuel tank is between 1/4 and 3/4 full. Engine coolant temperature must be below 122°F and within 11°F of the ambient air temperature.
B. Idle. Run engine (do not drive) for 2 1/2 minutes with the accessories off. Put the vehicle is Drive (D) while pressing the brake pedal, and hold for 15 seconds. Put the vehicle in Park and turn the ignition to OFF position. Repeat this step once. The ECU will run the Oxygen Sensor Heater self-test and EVAP Purge "No Flow" test.
C. Start the vehicle and turn all accessories off. Begin to drive. Apply half throttle until 55 mph is reached. The ECU will now begin the EVAP Purge Flow test.
D. Hold your speed steady at 55 mph for five (5) minutes. During this time the Oxygen Sensor O2 response, Air Intrusive (AIS System), EGR Flow, Purge Valve, Misfire Detection, and Fuel Trim diagnostics will be performed.
E. During this step slowly let off the accelerator pedal. Do not brake or shift in order to slow down. It is important to let your Montero coast along gradually slowing down to 10 mph. The ECU will once again self-test the EGR System, EVAP Purge System and Long Term Fuel Trims.
F. Accelerate again at 3/4 throttle until 55-60 mph is reached. This will perform the same self tests as during the first acceleration step.
G. Hold steady speed once again. This time at 55 mph for two (2) minutes. During this time the ECU will perform the catalyst monitor diagnostics.
H. Decelerate. This will perform the same diagnostics as in the first deceleration step. Remember not to press the brake or shift gears.
This ends the Mitsubishi Montero Drive Cycle. Performing the drive cycle at least twice, or using your scan tool check to see if one drive cycle set the EVAP monitor to "Ready".