They are thermally controlled. During winter in particular but any cold startup they will be closed to restrict airflow to the radiator to push coolant and oil temps up to operating temp. Because a hot engine is an efficient engine. Cold oil is less viscous and essentially has drag within the engine.
They do also have a little effect on aerodynamics but I think it's so marginal. And that would also require a certain speed for them to close and it would have to calculate engine load because if they close at highway temps towing you're going to overheat...
SO really I think the only function is warmup.
BUT the shutters only are on the upper portion of the grill. Not the entire thing.
Aerodynamics plays an important role with
regards to fuel efficiency. Aerodynamic drag
increases as vehicle speed increases resulting
in increased engine power requirements.
Reducing wind drag coefficient across the front
of the vehicle is directly proportional to an
improvement in fuel efficiency.
That’s where the Active Grille Shutter System
(AGS) comes into play. It is designed to reduce
The AGS system is located behind the front grille
on a number of our vehicles, Ram 1500,
Cherokee, Dart, and the new 200. The system
consists of an electric stepper motor (actuator),
a set of vanes that make up the shutter, linkage,
and a set of seals that direct air flow.
The AGS system is controlled by the powertrain
control module (PCM) over a dedicated network
LIN bus. The PCM commands the AGS to
regulate airflow across the radiator or to
improve the vehicles drag coefficient. When
airflow is not required and/or vehicle speeds
reach a threshold, the PCM commands the
shutter vanes to close. If additional cooling is
required the PCM commands the grille shutter
vanes to open. In cold climates, the AGS
system can improve engine coolant warm-up
times further increasing fuel economy.
Each time the vehicle is started the AGS
performs an initialization calibration. This
function can be used as a quick way to validate
the operation of the AGS. To validate AGS, start
the engine and observe the AGS shutter, the
vanes will cycle to the fully open position and
then move to the fully closed position. The AGS
uses this procedure to learn the hard stops on
the grille shutter frame for that key cycle.
The AGS actuator contains an integral smart
module that uses the LIN bus to communicate
with the PCM. It receives shutter position
commands from the PCM and reports its
position to the PCM. The AGS communicates a
series of faults to the PCM.
If the AGS smart module detects the grille
shutter vanes are jammed, it will attempt to free
them by cycling the shutter from the open to
closed positions 3 times. If this condition is
detected when the ambient air temperature is
greater than 4.4° C (40° F), the MIL will
illuminate and a fault will set. If the
ambient air temperature is below 4.4° C (40° F)
and a jammed condition is detected, the smart
module will assume the shutters are frozen and
will not illuminate the MIL or set a fault.