1996 Chevrolet Silverado, what does it mean fuel system 1 closed?

Question

when u a hook a code reader up to it shows that fuel system 1 closed what does it mean

Answer 1

Fuel system closed, that means the 02 sensor is in closed loop and the ECM sees its, At one time OBD 1 and early model of OBD II used the coolant temperature , when it reached operating temperature the system would go to close loop. Being at operating temperature for the coolant temperature , the 02 sensor would drop out of even though a heater was added to the 02 sensor. Fuel system is a important data  this means the heater is at operating temperature and the ECM responds to if. When it is a open fuel system the ECM does not see or use the 02 sensor. If the engine is at operating temperature and a open system you will set a P0130 for that Bank