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I talked to a pretty knowledgeable CT5-V BW owner that often tracks his car, that said the sensor doesn't really read pad % as it states in the manual. Instead it is like the scraper. Once you wear down the pad and the sensor and expose the metal in the sensor it completes a simple circuit that will trigger a warning message in the DIC.
So basically an idiot light. That would also make it easier to tie off, since the open state is "everything's fine!" Unlike most German pad wear sesnors where unplugging them will set off the idiot light. Good to know.
 

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Discussion Starter · #22 ·
Yes, the owner's manual talks like it will give you a % in the Maintenance section of the DIC, but mine didn't and certainly doesn't now with the sensors tied off. I don't have any idiot lights or warnings showing either.
 

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2023 CT4V Blackwing 6MT (ordered)
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Thank you for going through the trouble of getting the detail and part numbers. That's super helpful. I think when I get my 4BW, I'll swap to low dust pads for DD and stock pads for track days to keep dust to a minimum. The BW has a brake by wire system though, which uses tables calculated during development versus temp sensors, etc to keep pedal feel the same from lap 1 to lap 10, but those tables were calculated with stock pads. I'd be concerned doing track days with aftermarket pads that have different fade characteristics.

Savagegeese does a great job explaining this in their CT4V BW video on YouTube. There's info overlap with their CT5V BW video as far as systems shared between the two cars. Highly recommended as they got lots of data from both GM engineers as well as Brembo engineers.
 

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Thank you for going through the trouble of getting the detail and part numbers. That's super helpful. I think when I get my 4BW, I'll swap to low dust pads for DD and stock pads for track days to keep dust to a minimum. The BW has a brake by wire system though, which uses tables calculated during development versus temp sensors, etc to keep pedal feel the same from lap 1 to lap 10, but those tables were calculated with stock pads. I'd be concerned doing track days with aftermarket pads that have different fade characteristics.

Savagegeese does a great job explaining this in their CT4V BW video on YouTube. There's info overlap with their CT5V BW video as far as systems shared between the two cars. Highly recommended as they got lots of data from both GM engineers as well as Brembo engineers.
The brake by wire is a big question mark with aftermarket pads. I'd like to think GM's engineers were smart enough to make the system dynamic and able to read g forces and speed to measure whether or not the pads are performing as expected. That's a complete assumption, though. It may be a dumb system based on application counts and pressure, with no accounting for actual braking performance.
 

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Good video describing the system basics.

Since the car doesn't have brake pad temp sensors, the pad temps can be inferred in the modules by observing what is actually happening during a stop. If the system has a good look up table of brake pad mu vs pad temp and uses feedback from the accelerometer and brake system hydraulic pressure that was needed to produce that measured deceleration value during a stop and does a look up on the mu vs temp table, the system can estimate the current pad temp by comparing the actual measured deceleration rate vs the amount of hydraulic pressure needed to reach that measured deceleration rate. It can also use those values from the the previous brake application in a feed forward loop to adjust the booster assist amount as needed to maintain a fairly constant pedal pressure and travel input for a desired deceleration rate on the next brake application. It can also use data from the vehicle speed, ambient temp sensor, the previously calculated pad temp during the last brake application, and time driven since the last time the brakes were applied to estimate how much the brakes have cooled since the last application and adjust the booster accordingly.

Also, if the system sees a lower deceleration rate than expected for a given amount of hydraulic pressure output, it should be able to infer that the brakes have faded and pop up a warning message for overheated brakes (and possibly also limit vehicle speed and engine power until the brakes have cooled-- depends how safe GM wanted to play things.)

Having the e-booster trying to maintain consistent pedal input force and travel vs desired deceleration amount as the brakes heat up is nice, but IMO it also removes a key piece of driver feedback that a standard master cylinder setup offers-- how the pedal feels in terms of effort and travel changing when the brakes start to overheat and go away. As long as the e-booster is adjusting trying to maintain constant pedal effort and travel to produce a given deceleration rate regardless of brake pad and brake fluid temp they've removed that feedback to the driver through the pedal about the pad condition, and now you're relying on the software to throw up a warning on the dash if the brakes start to overheat and go soft.

With aftermarket pads having different mu values than the stock pads the tables regarding expected deceleration rate / hydraulic pressure vs pedal input force are going to be off, but at least you have 3 levels of brake assist feel to choose from in the drive modes. If your new pads have a high mu value that's greater than the stock pads and the brakes are very touchy you could set the brake feel in the drive mode to full soft to take the edge off them, or on the other hand if you change to a low dusting pad which has lower mu values than the stock pads and the pedal feels a bit soft you can increase the assist/pedal feel in the drive mode selection.

My main concern changing pads would be the overheat detection in the stock software. If you run specific track day pads with a high temp capability and a higher mu value than the stock pads the system will probably not throw any warnings as the pads will keep generating good deceleration rates vs the applied hydraulic pressure even as the brakes get hot (unless there's a separate failsafe parameter that throws up a brake overheat warning after X number of hard decelerations in a certain amount of time regardless of what the accelerometer and hydraulic pressure numbers are saying), but if you run say low dusting ceramic street pads with a lower mu value and a lower max temp capability than the stock pads and go out for a hard drive I could see the system throwing fade/overtemp warnings on the dash earlier than expected as the ceramic pads start to fade at a lower temp than the stock pads and would start to require extra hydraulic pressure to produce a desired deceleration amount compared to the stock pads. Pads with a really, really low mu value that require a lot of hydraulic pressure to decelerate the car may throw an overheat warning even when the pads are cool.

Without knowing the exact thresholds GM set in the programming, it's hard to say for sure. I'm guessing there's enough wiggle room in the software to handle aftermarket pads with reasonable mu values without throwing up warnings, especially if used for street driving.
 
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