Loop Status (O/L - C/L)

This position indicates whether the engine control system is operating in open loop (O/L) or closed loop (C/L) mode. Most systems are designed to enter closed loop after a certain amount of run time, when the coolant temperature exceeds a specified value and the oxygen sensor (O2) begins to function. This mode can be helpful in detecting intermittent opens in the O2 sensor circuit, as the SCAN tool will indicate open loop operation long before the appropriate trouble code will be set in the Electronic Control Module (ECM)memory.