The HEGO maintenance timer is located under the dash, driver's side, to the right of the steering column. It is a one-use only timer, about $60 to replace at the dealership parts counter. Just unplug the timer, the light will go out. It is a reminder to replace your o2 sensor, just track your mileage.
ParadiseXJ and JJacobs are right--real-time only system so no stored codes and no CELs.
Possible names for the engine management other than Renix: OBD-0; OBD-Less. Any other suggestions?