Here’s Why Busted Plastic Grille Flaps On A Newer Car Can Cause A Check Engine Light

The check engine light is one warning most drivers dread. In many counties, it means a vehicle may not pass OBDII-based emissions testing, and you typically need a valid emissions test to register a vehicle in clean air areas. While all manner of issues from failed catalytic converters to a loose gas cap can cause the check engine light to glow, there’s a relatively recent annoying potential culprit to keep an eye on — a bad set of active grille flaps.

Technically, these aren’t usually in the plastic grille you see, but instead are a separate plastic grille just behind the main unit. So, how do these active grille shutters work, why would a malfunction trigger a check engine light, and how widespread are issues with these fancy pieces of plastic? Let’s dive into it, starting with that first question.

Over the past 90 years or so, automakers have grown more and more eager to cut drag in their new models. From the Chrysler Airflow to the super-slippery Lucid Air, a huge component of efficiency is being able to cut through the air cleanly with as little resistance as practical. Drag is the reason why some cars hit their top speeds long before they run out of gearing or into a limiter. Drag is also the reason why some pickup trucks come with goofy front air dams. Lower the drag, increase economy, and theoretically, everyone wins. The engine bay of a car is one turbulent area, so by blocking off the grille under certain conditions, a vehicle should become more aerodynamic.

While different automakers use different logic for their active grille shutters, on combustion-powered vehicles, the operating principles usually work a bit like how Nissan programmed its active grille shutters to operate. As per the Japanese automaker:

The active grille shutter is fully open when the vehicle stops or the ignition switch is turned OFF. The ECM operates the shutter to the closed position in order to perform shutter initial position learning when the ignition switch is turned ON. At the end of the initial position learning, the ECM operates the shutter to the open position until the vehicle speed reaches approximately 14 MPH. (The initial position learning is performed every time the ignition switch is turned OFF → ON.) While driving, after the initial position learning ends, the ECM operates the active grille shutter to the closed position when the vehicle reaches a specified speed for the first time. The ECM operates the shutter to the closed position when all the conditions of the active grille shutter are met: vehicle speed (approximately 19-88 MPH), engine coolant temperature (approximately less than 203°F), engine oil temperature (approximately less than 284°F), CVT fluid temperature (approximately 275°F), cooling fan ON and refrigerant pressure at 1.18 MPa or more. If the vehicle is driven at a high speed, the ECM operates the shutter to the open position when the vehicle reaches the specified speed of approximately 88 MPH in order to prevent the shutter from closing due to wind resistance. When the vehicle speed is reduced below the specified speed of 88 MPH, the ECM calibrates the active grille shutter to the closed position and then to the open position when the vehicle speed is less than 14 MPH.

When a vehicle’s switched on, cycling usually occurs to ensure that the active grille shutters still work. At extremely low speeds with airflow through the radiator being largely limited by what the cooling fans can push or pull, these active flaps stay open to prevent overheating. However, once a vehicle with active grille shutters starts moving and all fluid temperatures seem fine, the flaps close to smooth out the front end and improve the vehicle’s aerodynamics. If temperatures or speeds get too high, the grille flaps then open again to promote airflow and prevent themselves from being stuck. Makes sense, right?

So, why would these shutters set off a check engine light if they stop working? Because active grille shutters affect vehicle aerodynamics, they are considered pieces of emissions equipment. The EPA currently offers Corporate Average Fuel Economy credits if active grille shutters provide a reduction in drag, so all manner of automakers from McLaren to Subaru are hopping on the bandwagon. In theory, these moveable plastic grilles are great, helping engines warm up quicker and aiding in the pursuit of aerodynamic efficiency. However, if moving plastic parts on the front of a vehicle sounds like a recipe for problems, your intuition isn’t exactly wrong.

What can cause these active grille shutters to malfunction? Well, the actuator could pack up, the wiring could develop a fault, or, as Nissan puts it in a technical training article, obstructions may occur.

Service Tip: Debris or snow caught in the shutters may prevent proper system operation.

Ah, yes, snow. You know, the natural phenomenon that tens of millions of North Americans experience seasonally. This is like when heavy rain overwhelms forward-facing RADAR units, except “automatic emergency braking unavailable” doesn’t trigger a freaking check engine light.

Even worse, issues with these active grille shutters happen all the time. The active grille shutters on many early 2017 BMW 7 Series and 5 Series models are crappy enough that BMW has extended warranty coverage on the components for 10 years or 120,000 miles, as per technical service bulletin SI B01 01 19, and Nissan has a whole set of instructions for the Versa Note’s active grille shutters that I mentioned earlier. Oh, and that’s before we dig into owners’ forums, where drivers across multiple makes and models report having problems with their grille flaps.

Maybe it’s just me, but this forum post from a 2022 GMC Sierra owner reporting active grille shutter problems with just 800 miles on the clock doesn’t seem particularly confidence inspiring. It’s certainly not the only forum post about active grille shutter issues on GM trucks, with trouble codes being reported over two generations of full-size pickup trucks.

What about across town at Ford? Well, F-150 owners are also reporting active grille shutter problems. The above forum post comes from the owner of a 2019 F-150 with the 3.5-liter Ecoboost V6, and several F-150 diesel owners in the same thread report similar issues. Mind you, the F-150 isn’t the only Ford product in which owners are reporting active grille shutter failures. Just check out this post from a 2016 Explorer owner below.

Alright, so we know that BMW’s had issues with active grille shutters, Nissan has published an entire diagnostic tree, and domestic vehicle owners report issues, but what about owners of Japanese cars? Well, previous-generation Honda CR-V owners are reporting fairly widespread issues with grille shutters, with the forum post below being merely one of many scattered across CR-V owners forums.

As for Toyotas, grille shutters can fail on those things too. The Camry Hybrid is a model for robustness, the de facto taxicab from Sydney, Australia to Sydney, Nova Scotia. We’re talking about a vehicle that’s built to last, so any unusual failures like this owner’s active grille shutters are worth cocking an eyebrow at.

Adding insult to injury, paying to replace these active grille shutter units can potentially wipe out fuel economy savings. Directly from Nissan, the active grille shutter assembly for a 2017 to 2019 Versa Note carries a suggested retail price of $363.64. That’s just the part, no labor. The Explorer owner several posts up the page claims a repair quote of more than a grand, and shutters for a half-ton Silverado go for $324.99 at Autozone.

While cutting drag with active grille flaps can gain regulatory credits, promote quicker engine warm-up, and save drivers some cash at the pumps, replacing active grille shutters can be a pain. In a climate as varies as North America’s, the promotion of such a technology seems a bit like theory trying to assert superiority over practice, with predictable results. As vehicles with active grille shutters age past a manufacturer’s parts support period, one can reasonably assume that bad active grille shutters may send vehicles to the junkyard if good replacements dry up. We’re really looking at unnecessary complexity for the sake of regulatory kudos, a neat but flawed idea that’s made it under the hood of many vehicles.

(Photo credits: EPA, Nissan, GMC AT4 Forum, F-150 Forum, Explorer Forum, CR-V Owners’ Club, ToyotaNation)

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