Active Grille Shutter Module

Operates movable vanes behind the front grille that close off airflow to the radiator when cooling is not needed. An open grille is a large aerodynamic penalty — air entering the engine bay and tumbling out is drag — so closing it when the engine is cold or lightly loaded measurably improves economy and warm-up time.

Two failure positions, with very different consequences, and establishing which applies is the whole diagnosis. Stuck open is benign: slower warm-up, slightly worse economy, a slower cabin heater. Stuck closed matters — the radiator receives a fraction of the air it needs, and while the fan can usually cope at low speed, under sustained load (a long climb, towing, motorway speed in summer) it cannot. The temperature gauge is the instrument. Most vehicles default the vanes open when control is lost, precisely so this cannot happen — but a mechanism jammed by debris or ice does not obey that default.

The causes are unusually environmental. These vanes sit in the airstream at the very front, collecting plastic bags, leaves, road salt and stones in the linkage. And in winter slush thrown into the grille freezes them solid — extremely common, seasonal, and leaving the mechanism completely undamaged. A code in freezing weather is worth re-checking after the vehicle has thawed before anything is replaced.