What value indicates when the vehicle has warmed enough for the PCM to operate in closed-loop?

What value indicates when the vehicle has warmed enough for the PCM to operate in closed-loop?

• A. Engine Coolant Temperature
• B. Minimum Temperature
• C. Hot Idle
• D. Air-Fuel Ratio

Answer: (A)

Closed-loop fueling begins when the engine has warmed up enough for the PCM to rely on feedback from the oxygen sensors. The signal that tells the PCM that warmth level is reached is the engine coolant temperature. Once the coolant temperature reaches the appropriate threshold for that vehicle, the PCM switches from open-loop (where it uses pre-programmed fuel maps) to closed-loop, using the O2 sensor readings to fine-tune the air-fuel mixture toward the target ratio. The other options aren’t indicators of warmth: minimum temperature isn’t a standard trigger, hot idle is a operating mode rather than a warmth signal, and the air-fuel ratio is the target of the control, not the trigger that starts closed-loop.

Closed-loop fueling begins when the engine has warmed up enough for the PCM to rely on feedback from the oxygen sensors. The signal that tells the PCM that warmth level is reached is the engine coolant temperature. Once the coolant temperature reaches the appropriate threshold for that vehicle, the PCM switches from open-loop (where it uses pre-programmed fuel maps) to closed-loop, using the O2 sensor readings to fine-tune the air-fuel mixture toward the target ratio. The other options aren’t indicators of warmth: minimum temperature isn’t a standard trigger, hot idle is a operating mode rather than a warmth signal, and the air-fuel ratio is the target of the control, not the trigger that starts closed-loop.