Jim theorizes that low coolant
caused portions of the engine to get too hot, so the temperature sensing computer thought it was very cold outside, and made the fuel - air
mixture too
rich (less air).
Neither should damage the catalytic converter irrevocably (except perhaps alternating lean -
rich mixture could
cause potential damage, if the carbon -
rich compounds stay in the catalytic converter semi-permanently and then the oxygen -
rich compounds arrive to allow the chemical reaction to proceed — now, could this happen if your sensor is damaged, I'm not sure, perhaps somebody more experienced in cars could answer).