Which of the following is NOT an indication of a catalytic converter problem?

The stability of the catalyst monitor signal typically indicates that the catalytic converter is functioning properly. A stable signal means that the converter is effectively converting harmful exhaust gases and maintaining its efficiency. In contrast, signals that fluctuate or show erratic patterns could suggest that the converter is failing or clogged, as it would struggle to process exhaust gases correctly. Each of the other options represents potential signs of a catalytic converter issue. A bluish shell can indicate overheating and potential damage, a rattling noise often suggests that the internal components are broken or not securely in place, and little difference between inlet and outlet temperatures can signify that the catalyst is not working as intended. Hence, the stable catalyst monitor signal stands out as an indication of good performance rather than a problem.