Hello fellow Bolters,

For some time now, I have had "Service Park Assist System" appear on the display when I put the car in reverse or when the driving speed drops below 6mph or so. The assistance systems do not work, there are no sounds. Cleaning/checking the sensors did nothing. Rear camera with guidelines works fine.

There are no DTCs logged (checked with 2 different OBD2 devices).

Yesterday I went to the dealer, he connected his GM MDI 2 scanner, the result was a bit baffling:

The sensors are all fine, but the scanner reports that it can't communicate with the the brake booster module. The technician thinks it'* related, but I'd have to make an appointment and leave the car at the shop for 1-2 days to get an accurate diagnosis.

It all seems strange to me.... The fuses are all ok and the brake booster control module can certainly communicate with other modules via the vehicle network - as soon as it or the brake pedal sensor are disconnected the car throws the corresponding DTCs, which can then also be cleared via the OBD interface when the module is reconnected.

A workshop visit of several hours just to hear that the brake booster ($1000+) needs to be replaced doesn't really sound that appealing to me, maybe someone has some experience or another idea?

Thanks!

It probably won't run the parking assist system unless all related modules are communicating sanely. It could be that the module is communicating with the system, but what it is telling the system isn't "sane" compared to what it expects during equivalent circumstances. GM'* engineers, beancounters, and lawyers likely all agree that they want no part of a system that moves the car that doesn't know what it needs to know about whether or not it can stop the car.

Makes sense. I bet there are odd (not sane) readings being seen while the modules are otherwise connected and communicating. When you are dizzy, you still function and feel balance, but the balance is wrong and you know by doing a sanity check with your other senses (sight mostly, and feel at your feet and legs). It is at this point that your Bolt would disable your balance system and then warn you so that you know to go by sight and feel alone.

. . . and if you keep getting dizzy, a visit to the doctor would be in order. Also probably not too appealing.

Back in the day, mechanics would repair generators in automobiles. They'd literally pull them out, put them on a bench, take them apart, measure stuff with a micrometer, maybe machine the armature, install new brushes, solder wires in place, etc. It was an art, and some were better at it than others. Replacing a generator was almost unheard of. Then, alternators came along, then rebuilders came along and now just about nobody repairs alternators in the field. It is just a part swap, and the actual work is done by some faceless specialist far far away. Some are better at it than others, but their results are much more measurable therefore correctable. In general, this keeps the result pretty consistently good.

Fast forward to your car. This part was never field repairable like many parts on many cars today. It is a relatively simple module that does a specific job, nothing on it can be repaired, and the operability of the module is monitored by many lines of code in a computer that is not part of the module. Those lines of code are dispassionate and fairly inflexible. When a parameter falls outside of an acceptable range, it has an action programmed in that it must do, and then it does it. Period. End of story. It doesn't agonize over the meaning of it'* decision because there isn't a decision as far as it is concerned. "If I see this condition I take that action". The code that handles this was written based on engineering decisions made before the car went into production and is only changed by firmware updates. The brain doesn't even know it is involved in any way with being a car. It just knows "if this then that". In your case, I bet it is something like "I see this telemetry, based on this telemetry I change this bit over here from a '1' to a '0' . . . and in a separate thread "if that bit over there is "1" then run the subroutine for [enabled], if that bit over there is '0' then run that other subroutine for [disabled]."

Greatly oversimplified but this is how it works.

You could swap the part out yourself and see what happens. I'm not sure if it needs to be locked to the vehicle'* VIN like many modules do. In the end, I suspect a visit to a dealer or a really advanced independent shop will be in order, and since the Bolt is relatively rare, it will appear to be a more exotic repair to most technicians.

Thanks for your comments,

I understand and agree with everything you say, these are also my conclusions. The brake booster control module is part of the brake booster unit, and a new (expensive to buy and fit) brake booster unit needs to be calibrated after installation with a special procedure which requires specialist GM hard- and software. I cannot do this myself, although board-level electronics repairs and ICE teardowns are not scary for me. Spending thousands to get back a feature that is not really a safety improvement, just a comfort feature, is not my priority.

I was really hoping for someone who had had a similar experience to say "Ah, it'* probably the tension on the doo-dah just there, try reconnecting cable harness such-and-such after a full reboot" or some such...

Ah yes: "Captain Picard to the Bridge! Captain, we've got a problem with the warp core, or the phase inducers, or some other damn thing."

I've never heard of this particular problem. This is probably about the third Bolt that'* ever shown up here with problems.