Ask a Mechanic: Side detection system’s problem may be corrosion

Dear Ask a Mechanic,

I own a 2015 Chevrolet Malibu. Several months ago, I clipped my side mirror against my garage, breaking the mirror and damaging the door. After getting it back from the body shop, every time I start the car there is a warning to service the side detection system and the warning light on the mirror doesn’t work properly.

I took it back to the garage, and it insisted that the warning has nothing to do with the mirror it replaced. The garage said that I must take it to the dealer to get it fixed. Everything worked fine before I broke the mirror, and I think that the garage is trying to pass the buck. What do you think? – Feeling blindsided

There are several possibilities here, but I will start by correcting a common misconception that the mirror is involved in sensing vehicles that are in your blind spot as part of the side detection system. It is not. The side mirrors only purpose is to visually show the driver what is behind their vehicle when they are properly adjusted. It just happens that the mirror is also where the vehicle’s designers placed the warning light about issues with the side detection system.

The sensors that do the detecting are mounted at the rear corners of the vehicle, most of the time either behind the bumper cover or in the taillights. In the vehicles I have worked on, both the sensor and electronic module are found in one unit (like a box).

These units are installed in a vulnerable location, not only susceptible to damage during even minor fender benders, but often exposed to moisture and salt. Certain models have known issues with corroded modules due to water.

General Motors released a bulletin about this issue in several makes and models in 2019. While the Malibu was not included on the list, it is still possible this could be the issue as the module in your vehicle is in a location similar to that of the Impala, which is mentioned in the bulletin.

There is a service kit available for certain Impalas that includes a pair of modules, the wiring sub-harness – which often gets destroyed by corrosion – and protective covers. This kit does not apply to your Malibu, unfortunately, and diagnosis will still be required to confirm my suspicion that the module wiring in your vehicle has corroded. If this is the issue, your vehicle’s new modules will need to also be programmed so they will function.

Ask a Mechanic is written by Brian Early, a Red Seal-certified automotive technician. You can send your questions to wheels@thestar.ca. These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your vehicle.