If you’re an owner of a Cadillac Escalade, Chevrolet Silverado, or GMC Sierra from model years 2019 to 2024, you might have noticed something peculiar about your truck’s mirrors during those frosty mornings. One mirror defrosts considerably quicker than the other.  Before you jump to conclusions about something being defective, let’s dive into the intriguing engineering behind this phenomenon – as detailed in the Technical Service Bulletin (TSB) 23-NA-167 from September 2023.

An Unequal Case of Two Rear View Mirrors

GM is seeing some customers worried that their side view mirrors heaters could be defective. TSB 32-NA-167 notes: “Some customers may notice that the outside rear view mirror defog or defrost times maybe different for the passenger and driver’s side mirrors.”

You’ve probably seen this happen yourself now that fall is upon us and colder mornings are more normal. I personally saw this happen to us on our 2022 Chevrolet Silverado ZR2 a few mornings ago when a heavy frost blanketed the front windshield and mirrors after a hard frost and 18-degree temperatures hit. Pulling out of my driveway it was easy to see the passenger mirror defrosted far quicker than the drivers side. My first reaction was something might be wrong with the driver’s side defroster.

A Tale of Two Mirrors: The Why And How

But as it turns out, in the world of T1 trucks and SUVs, not all mirrors are created equal – and you may have never even thought about why.  The driver’s side mirror, with its advanced Electrochromic glass, is a hefty 4.05 mm thick. This isn’t just any glass; it’s a sophisticated concoction of liquid and glass designed to dim reflections and combat glare, a real boon for driving safety. But, this innovative feature has an interesting side effect: it takes a tad longer to defog due to its greater mass.

On the other side, the passenger mirror is a leaner 2.00 mm thick and skips the Electrochromic liquid. The result? A quick defrost. In just 3 minutes, it’s 98% defogged, while the driver’s side reaches 80% clarity in about 6 minutes.

Not a Flaw: Embrace the Difference

Now, you might be thinking, “Is my truck’s mirror defroster broken?” Rest assured, it’s not a problem but a testament to GM’s thoughtful design. This difference isn’t a defect; it’s an intended feature that aligns perfectly with GM’s intentions. The official GM spec is 80% defrosted in 6 minutes, so the driver’s side is performing as designed even if it doesn’t look like it.  The defogging process being different for each mirror is simply a factor of the increased mass and thickness of the driver’s mirror.

How to Test Proper Operation Yourself

How do you know your mirrors heated mirrors are working properly? Simply activate your truck’s rear window/ side view mirror defrost button and give it around 6 minutes. Feel that temperature change? That’s the sign of a perfectly working heater element – a reassurance that everything is as it should be.

Why This Matters – No Trip To The Dealer Needed

Understanding the “why” behind your GM truck’s unique mirror defogging rates not only puts your mind at ease but also highlights the innovative approach GM takes in designing vehicles. It’s a conversation starter, a snippet of cool trivia to share with fellow truck enthusiasts, and a nod to the fact that sometimes, what seems like a problem is actually a stroke of genius in disguise.

So next time you notice the defrost discrepancy, remember – it’s not a bug; it’s a feature. Embrace the “hot” science behind your GM truck and hit the road with confidence that you don’t have to take a trip to the dealer for a warranty claim.