Hello ,We have a 2005 Nissan Sentra the "Service Engine Soon light went on". So we took it in and the Mechanic said it had a code P0420 The mechanic replace the main catalyst converter with a rebuilt one. After driving it the next day the light went on again. Took it back and he replaced the Catalyst Converter with another rebuilt one. Dash light went on again, this time he replaced the other converter. Next day, light went one again. This time he replaced the O2 sensor. That evening the light went on again....HELP Frank
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