emmission codes on 1997 Chevrolet Monte Carlo

do u know what the code po121 means for 97 monte carlo 3.1 v6? or po420 on 98 merury sable?

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1 answer
The p0121 on the monte carlo is a throttle position fault. More testing would be needed to determine if the sensor is actually bad. The p0420 on the mercury is a catalytic converter fault. Most likely indicating the converter should be replaced.