Rear and side-view mirrors used to be simple bits of shiny glass that let you see what was coming up behind your car. These days, they're full of all kinds of electronics that, unsurprisingly, can make them rather more fragile than they used to be. The Corvette C8 has fallen victim to this curse, with General Motors issuing a bulletin on the issue.
Update: 12/13/21 3:22 a.m. ET: The post has been updated below with comment from GM.
The problem concerns the driver's side mirror on 2020-2022 C8 Corvettes. As per GM's Techlink bulletin, the mirror "may have poor operation and appearance, including numerous lines shown in the mirror and a dim reflection at all times." The bulletin notes that the problem "may be caused by the installation of an aftermarket radar detector in the vehicle. Depending on the installation location, the aftermarket electrical device may cause higher voltage to the mirror."
Aftermarket radar detectors are often installed just below the rear-view mirror in the center of the interior. In the case of the Corvette, it is apparently common practice to tap in to a connector in this area to power the device. This then interferes with the power going to the driver's side mirror, causing the problem.
It's unclear as to the precise issue that causes the visual flaws in the mirror. One theory is that excessive voltage applied to the heating elements for the defrosting feature could cause cracking or other damage to the mirror, leading to the telltale pattern seen in the bulletin.
Alternatively, as seen in a forum post from 2020, the auto-dimming feature on the mirror could be the culprit. This consists of a special electrochromic gel placed between two glass plates in the mirror. The amount of light allowed to pass can be controlled by changing the voltage applied to the gel. If the wrong voltage is applied to the gel, this can cause damage.
The caveat is that this forum post does not contain any mention of a radar detector installation. Interestingly, others have had issues with mirror-mounted radar detectors blocking the light sensor for the system, causing the mirrors to dim all the time. A possible explanation could be that a blocked light sensor could cause the dimming system to run at an excessively high duty cycle, eventually "burning out" the electrochromic gel.
Either way, it seems that the "X1" connector that is commonly tapped into to supply voltage to radar detectors is not a suitable source of 12V power, as it can interfere with some electronics in the driver's side mirror. GM's bulletin instructs dealers should check behind the central rear-view mirror for an aftermarket jumper harness if the side-view mirror shows this type of damage. It also notes that such damage caused by the installation of aftermarket accessories is not covered under warranty.
The Drive has reached out to GM for further comment regarding the exact cause of the issue, as well as its prevalence in the wild, and will update as information becomes available. In the meantime, if you've got a radar detector installed in your C8 Corvette, consider checking that it's been installed in a safe and proper manner.
Update: GM has clarified the nature of the issue, with a spokesperson telling The Drive that installing a radar detector using the X1 connector "creates an issue with the dimming circuit, resulting in lines in the mirror and dim reflection at all times." Reportedly, GM has seen "very few" of these issues in the wild.
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