Highway Fuel Mode (Semi-"Closed Loop")

Highway Fuel Mode (Semi-"Closed Loop")
This mode comes into operation at highway speeds and its purpose is to improve fuel economy. For the control module to operate in this mode, it first must sense the correct engine coolant temperature, ignition control, canister purge activity and constant engine speed. During semi-"Closed-Loop" operation, there will be very little long term fuel trim (formerly known as "Block Learn") and short term fuel trim (formerly known as "Integrator"), and the heated oxygen sensor values will read below 100 millivolts.