Keep blind-zone system in good working order

Question: During the past several months, I’ve encountered a “side blind-zone system unavailable” warning while driving my Chevrolet Tahoe. Since this only happened twice, I figured it’s not going to be very useful to take it in to the shop. Can you explain how this “system” works and what may be going wrong?

B.W. Answer: Your blind-zone warning system consists of left and right objects sensors, each concealed behind the rear bumper fascia (painted plastic trim at the bumper corners), driver and passenger door modules, and driver and passenger (outside) mirrors, which display the alert indicator.

Your sensors use radar (electromagnetic waves that bounce off solid objects and return an echo indicating there’s something there) to detect a vehicle or object approximately in the vehicle’s 3:00-5:30 and 6:30-9:00 o’clock positions out to about four metres, and post a serial data message that is received by the door module on that side. The outside mirror indicator is then requested by the door module. If the turn signal for that side is on, a more urgent flashing message is displayed. Other carmakers may use cameras in the mirrors to detect and classify objects or a combination of several methods to get this done.

Reliable sensor operation requires reasonably clear weather, a clean sensor surface, and an occasional object occurring to prove-out radar function. Heavy rain, dirty sensors, snow buildup or perhaps towing a trailer or attaching a bike rack may cause missing alerts or suspended operation. Also, if you are driving in area without roadside features, perhaps the desert, and no vehicles approach for a period of about 15 to 25 minutes, the system may indicate a disabled or unavailable message as it is uncertain of radar functionality. In this case the system will reinitialize at the next key cycle.

If your warning message incidents match one of the scenarios mentioned above, there might be nothing to fix, other than keeping sensor surfaces (and/or cameras, on other vehicles) clean. If not, a professional-grade scan tool can be employed to communicate independently with each sensor to prove-out consistent functionality.

Blind-spot warning systems can also be much more sophisticated, perhaps shaking the steering wheel or applying opposite-side brakes (gently steering the vehicle away) should you begin to turn into a presumably occupied lane. Honda’s system quickly brings up a camera view on the centre display of the appropriate blind spot as you operate a turn signal.

For those of us driving vehicles without this feature, try adjusting the side mirrors like this: Driver’s side: Lean left with your head almost touching the door glass, adjust the left mirror so the side of the car is barely visible at the right side of the mirror, or perhaps up to 1/3 of the total mirror image. Right side: Lean right, head near the centerline of the vehicle, adjust right mirror so the side of the vehicle is barely visible at the left edge of the mirror — or up to 1/3 view. Adding a small convex stick-on mirror in the lower inside corner of each mirror can also help mixing it up with a vehicle, object or pedestrian in our intended path.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, California. Readers can send him email at bradbergholdt@gmail.com; he regrets that he cannot make personal replies.