O2 SENSOR HEATER AFTER CAT _________________________________ (range ON/OFF) Indicates if the preheating of the after CAT OS is ON or OFF. O2 SENSOR HEATER BEFORE CAT _______________________________ (range ON/OFF) Indicates if the preheating of the before CAT OS is ON or OFF. O2 SENSOR READY ____________________________________________ (range YES/NO) Indicates whether the lambda regulation part of the ECM is ready or not (open/closed loop. This depends on the lambda sensor temperature and operating conditions of the engine. Under full load conditions, the ECM goes into open loop.