One problem related to o2 sensor has been reported for the 2001 Mitsubishi Montero. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2001 Mitsubishi Montero based on all problems reported for the 2001 Montero.
At 35000, the trunk door latch mechanism is broken. At 57000 miles check engine light lit, caused by spark plugs or spark plug wires open. Replace all plugs and wires at dealership, cost $300. Not covered by warranty. At 77000 miles, check engine light lit, dealership replaced catalytic converter under warranty but I pay for the oxygen sensor plus labor that goes with the catalyst. Old parts not available. Car driven about 3 miles home from dealeship after replacing the cat. Converter, the check engine light lit again. Dealership checked and said another oxygen sensor is bad. Total 4 oxygen sensors in the system. Cost $230 to replace one sensor. I could not believe that these sensors will go bad at the same time. Is that a coinsidence or manufacturer parts defects???.