U0285: Lost Communication With Active Grille Air Shutter Module B
What to do
Watch the temperature gauge, especially under load — see U0284. With one set of shutters jammed shut the radiator still gets some air, so overheating is less likely than it would be otherwise, but you have lost cooling reserve exactly where it matters.
You can often see the fault yourself. With the engine warm and idling, look through the grille: your car has two sets of vanes, and if one set is open while the other is shut, that is the fault in plain sight — and it tells a workshop which module without any equipment.
If both sets have stopped, that is usually one shared fault — a fuse or supply feeding the front of the car — rather than two modules failing.
As at U0284, check for debris jamming the vanes and, in winter, for ice. The lower set collects far more of both, so a fault that keeps returning there is about where it sits rather than a poor part.
What this code means
The second active grille air shutter module has stopped being heard from. What the shutters do, and why stuck-closed is the case to watch for, is at U0284.
Two shutter modules means the grille aperture is split — commonly an upper and a lower set, or left and right — so that airflow can be regulated in stages rather than simply on or off.
The practical consequence is a partial one, and it changes the risk. With one set jammed shut and the other working, the radiator still receives some air, so overheating is less likely than with a single-module system fully closed — but cooling capacity is reduced, and the reserve that matters under sustained load is exactly what has been lost. The temperature gauge remains the instrument.
One thing specific to a split installation is worth checking and is visible from outside: the two sets should agree. Looking through the grille with the engine warm and idling, vanes open in one aperture and closed in the other is a direct sighting of the fault — and it identifies which module without any equipment.
And the counting test applies as elsewhere: both modules silent points at a shared supply or the network branch feeding the front of the vehicle rather than at two failures, which is the cheaper answer and worth establishing first.
The environmental causes at U0284 apply equally, and the lower aperture is the worse-affected of the two — it is closer to the road, collects more debris and takes more slush, so a repeated fault on the lower set is usually about position rather than about the part.
Likely causes
Start here
- Physical damage from road debris · moderate
- Airflow to the radiator face obstructed · easy
- Water ingress into the module connector · moderate
- Corroded or loose connector · easy
Less common
- Blown fuse or failed supply · easy
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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