The General has published a service advisory outlining a solution for some 2021 Cadillac CT4

small luxury sedans that may be impacted by an inaccurately calibrated Engine Control

 Module (ECM) that is possibly unable to detect and/or identify catalytic converter issues.

In certain situations, wireless over-the-air upgrades may appropriately recalibrate

the ECM software without requiring dealer repair, however potentially impacted 2021 

Cadillac CT4 cars should still be checked to confirm the issue has been resolved.

If there is a defect or failure in the car's catalytic converter in 2021 Cadillac CT4 units 

 with an inaccurately calibrated Engine Control Module, many difficulties may occur.

The ECM may fail to identify the defect by not lighting the Check Engine light, 

 may diagnose the catalytic converter problem inaccurately, or may fail to establish 

Diagnostic Trouble Codes (DTCs) so that diagnostic procedures do not discover the error.

This issue only affects Cadillac CT4 cars powered by the turbocharged 2.0L LSY I4 gasoline engine,