Loose Grounds Cause Strange Problems

A Honda Civic came into the shop with a very strange problem: the backup camera would turn on every time the brake pedal was pressed. It’s supposed to only show up when the transmission is in reverse. While looking at the car I also noticed that the gauge cluster wouldn’t know the trunk was open when the brake was pressed as well. There was definitely something going on in the wiring.

I started out by doing a basic visual inspection of the wiring harness in the trunk and in the trunk lid, where the camera is located. I noticed that some of the harness clips showed evidence of having been removed, so I knew that someone had done some kind of work on the car. The customer confirmed that the car had been in a rear end accident and gotten fixed at a body shop. It would be easy for wiring to get damaged in an accident, and may not get noticed during the repair process, so this made a lot of sense.

I began pulling the harness out to get better access at it so I could begin untaping it to check the actual wires to make sure none were damaged and shorting together. When I pulled more of the trunk carpet aside, I saw the main ground point of the harness, where it bolts to the body. As soon as I saw it, I could tell it was loose. I tightened the bolt, and the problems went away. When a component’s ground circuit is flaky due to a loose ground, it ends up grounding through wherever else it can find, which in this case caused other features to activate, like the backup camera.

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