scan with obd reader first

Two stages, if O2 sensor already not functioning, engine light will pop up intermittently or heading bad, permanently. This happened to my office pickup car, Triton with 300+k km, and SC Mitsubishi just put reset via reader, but the issues will return back. Until office guy send outside workshop and put new sensor, no more engine light pop.

On my car, since use it since new, kinda knows on what the FC average I get per refuel, and when passing 200k km, the FC kinda went worst. Done the normal EO change, atf oil, fuel filter, spark plugs but FC remain the same and not as new. Until change this O2 (my car had 2 of it), the FC restore back. Surprisingly able to hit 17km/l from JB - Kajang on meter, but at 110-120kmh consistent drive, quite tiring