[Cleaner]

Sean, my dealer's mechanic had the car but did not understand the problem. I requested we go for a ride together and he now understands the issue. He said the sonar sensors are acting way too sensitively. He said the TSB is not related to my issue. He said the service department would discuss with GM the issue because he would have to follow their authorizations to do this repair under warranty. I am still waiting for a response from GM. I will post again when the repair is done.

 

[Sean Nelson]

He said the sonar sensors are acting way too sensitively. He said the TSB is not related to my issue.

I have a sneaking suspicion that he's going to discover that the foam tape actually is the issue. I'm by no means an expert on this, but my guess is that the foam tape prevents the sensors from picking up internal reflections from inside the bumper, and if it's inadequate then you can get "false positives".

It's just a guess, though...

 

[ribbitribbit]

I'm experiencing this too. It's only happening on the passenger side; driver's side is working perfectly.

I got my Bolt in May, but the problem has only crept up in the last month or two. It seems to be getting progressively worse, as the weather gets colder.

Called the dealer today, explained the problem and pointed him at the TSB. He's ordered the magical tape and is going to call me once it arrives so it can be installed.

Fingers crossed.

 

[bbg523]

Well I can tell you I've been running my Foam/Foil tape modification for several weeks now and it surely has fixed my SBZA issues. The SBZA sensors work perfectly now.

Either Chevy needs to re-calibrate the sensors( heard someone had this done on the forum but have seen no TSB for it) or Provide more shielding around the sensors( formal fix vs what I did)

 

[bbg523]

BTW I did add a piece of Foil/Foam to cover the complete back of the Sensor. If you want to try this simple fix, I'd suggest you start with there first then expand out toward the wheel well if needed.

 

[Cleaner]

On another thread I have shared that I am waiting on GM for guidance. My issues with the blind zone alert come and go. After talking with the dealer (and they read the bulletin about the reflective tape) they concluded that it is a wiring problem. GM has a small TSB on this issue and instructed the dealer to examine the wiring to the mirrors and through the doors etc. They expect to find a loose wire or harness. Unfortunately for the last week it has not malfunctioned after a week of acting up non-stop. For me it is not the tape or a dirty car or snow tires or the cold. But I can't let them start taking apart everything until it acts up again.

 

[bbg523]

I'd still have them try the tape around the sensor first, It's a 15min fix. If it goes away, problem solved for you without having to rip into the car wiring.
Simple thing for them to try with little time involved.

 

[Eriamjh1138]

Great work bbg523! As it turns out, I installed a new winter tire/wheel combo last week and the problem started the same day. The new tires do stick out 1/4" more. Do you have a picture of where you installed the tape?

I was pretty liberal with the foam and tape. I just used some left over foam from my Seat Bottom upgrade.
It's about 1inch think, cut a piece 1'x1' and wrapped both sides with the foil tape and stuck it up next to the sensor between the wheel well.

It seems to do the trick.

I have inside information on the RADAR (not sonar, not lidar) sensors for the BOLT and here is what I can tell you about the SBZAs:


Each SBZA sensor is calibrated for the carline it comes with. Changing something as simple as wheels may cause false readings. Why? Because physics.

The radar signal that the SBZA sends out is very high frequency (24GHZ). It also is not 100% directed away from the car. Some of it goes backwards into the car. Because of the geometry of the Bolt, the distance from the rear wheel to the car body back to the sensor is very short. This had a tendency to cause rear reflections from the body to the wheel and back to be detected as false positive. On larger cars, it's not as challenging to overcome.

Look under the bumper and that butyl foil you see was the fix (already mentioned). It shields the sensor from the reflection. It's not perfect, but real metallic shields would not meet the bumper impact tests, so they stuck with the sticky butyl foil.

Notice that the LT and premier wheels look a lot the same? This reduces the need for a second calibration for each trim level.

So, the bottom line is adding or modifying the shielding is the best way to fix false positives. The shape may matter, too, so don't be surprised if your fix seems to work on one side, but not the other. If it shifts, so will the reflection, and so could the result.

That's all I can say and I don't have any other technical information other than previous posters were on the right track.

Don't bother the dealer with SBZA issues if you changed the wheels. It's your problem, now. The dealers just don't know it, yet.

 

[Sean Nelson]

I have inside information on the RADAR (not sonar, not lidar) sensors for the BOLT and here is what I can tell you about the SBZAs...

Great post, thanks. Do you have anything to substantiate your claim about these being Radar sensors? Because the sensors in the rear bumper sure look exactly like ultrasonic sensors to me.

 

[Eriamjh1138]

This is the sensor, is it not?

http://www.hella.com/microsite-electronics/en/Driver-assistance-96.html

And I was wrong. It’s 24GHZ, not 74GHz. The next gen is 77GHz.

 

[Sean Nelson]

This is the sensor, is it not?

http://www.hella.com/microsite-electronics/en/Driver-assistance-96.html

Yep, I totally agree that that's a radar sensor unit. But is it the one in the Bolt?

Sorry to be so obtuse about this, but what I see in the car looks like an ultrasonic sensor to me. I'm totally prepared to be wrong, but I need a bit more evidence than someone just saying so, because I repeat this kind of information to other people and I don't want to be misleading them.

 

[Eriamjh1138]

Well, I could ask you the same thing.

The difference is I know for sure and you’re guessing based on your experience. You can tell your friends “you heard it was radar”, and that would statement would be true (that I you heard it). They can decide for themselves and so can you.

 

[Sean Nelson]

The difference is I know for sure and you’re guessing based on your experience. You can tell your friends “you heard it was radar”, and that would statement would be true (that I you heard it). They can decide for themselves and so can you.

Well, yeah - that's exactly the point. I want to know for sure too - how do I find out?

 

[XJ12]

Yep, I totally agree that that's a radar sensor unit. But is it the one in the Bolt?

Sorry to be so obtuse about this, but what I see in the car looks like an ultrasonic sensor to me. I'm totally prepared to be wrong, but I need a bit more evidence than someone just saying so, because I repeat this kind of information to other people and I don't want to be misleading them.

The shielding on the Bolt seems to be more consistent with radar than ultrasound.

 

[bbg523]

The shielding on the Bolt seems to be more consistent with radar than ultrasound.

I agree it's radar based and most likely GM uses a calibration tool like- http://www.eoltest.com/sbza.html

 

[Eriamjh1138]

I now understand your position. The three “dots” you see in the bumper. Those are the ultrasonic sensors. Those are what you must mean when you say “they look like what I know to be ultrasonic” (paraphrasing).

You are correct. Those ARE ultrasonic sensors. However, those are only used for detection when backing up or moving slowly (possibly for other things). They are also relatively short range. You’ve seen the sensors working when you back up along a wall, near a trash can, or into another car on the dash (it’s the car emitting WiFi out its butt).

The side blind zone sensors are NOT those dots. The radar-based blind zone sensors are in the corner of the bumper and have no outward physical features on the rear fascia to give them away. You see their backside up in the bumper with that butyl foil against them. (That foil was a temporary fix and they still haven’t come up with a proper permanent solution!)

These sensors draw a 2d top-down view map and look for objects moving in and out of thef field of view. I’ve seen the “rough data” maps on demonstrations at tech shows and they look like 8-bit two-color, low resolution, blocky... maps. Cars and large objects like motorcycles and people can be detected. The software is smart and does not trigger an SBZA a wall, which looks like a non-moving object (there are other algorithms used for object detection). THe output of the sensor to the car is simply a CAN message saying Light-on or light-off. the map data never leaves the sensor (as far as I know. It is obviously available with development tools.

Are you more comfortable with the information, now?

 

[Sean Nelson]

The side blind zone sensors are NOT those dots. The radar-based blind zone sensors are in the corner of the bumper and have no outward physical features on the rear fascia to give them away. You see their backside up in the bumper with that butyl foil against them.

OK - I'll have to get down and look up under the back bumper to see what you're talking about. If I can find those sensors it will settle the matter for me - thanks for your patience!

 

[Eriamjh1138]

Bbg523 posted a picture of the radar sensor above. It’s to the right of his “fix” and above the factory foil.

Look in the corner of the fascia.

 

[Sean Nelson]

Look in the corner of the fascia.

Yes, I see it! OK, now I understand exactly what everyone is talking about.

Thanks!

Interestingly enough, on my Bolt (at least in the left rear corner, didn't check the other side) there's only a fairly small piece of metal tape that I can see on the bottom of the sensor - it's smooth and roughly shaped like a triangle.

 

[Eriamjh1138]

Some really early Bolts may have had a hand-made butyl foil cover while the tooling for the final shape was being made. That, or the factory messed up the install and tried to remove and replace the same strip, damaging it, etc.


We had to make a drawing and GM made a part number for each shield side. I think it is applied at the Orion factory as part of the bumper fascia assembly process.