Brake pressure PID?
 

Has anyone found the PID for brake pressure? I'm hoping to be able to log it with an OBD2 app and not need to get it via USB from a tuned ECU.

I would love to get this working as well. Aim can see it. Has anyone figured this out? OP are you using torque?

bump

I've logged brake pressure, steering angle and individual wheel speeds using OFT, but reviewing the data and overlaying them on videos takes a lot more work. Ideally I'm looking to do so via Racechrono/HLT/Torque. Or are those values limited to CAN mapping only?

Harrys Lap Timer (HLT) supports custom PID in their Beta V22 release, but I haven't figured out how to capture brake pressure. HLT V22 will estimate brake pressure from accelerometer data, if a custom PID isn't used.

http://forum.gps-laptimer.de/viewtopic.php?f=48&t=4907

I found this, but not sure how to implement it:
https://forum.autosportlabs.com/view...sc&start=0

Brake Pressure/Position

ID: 0xD1
Offset: 16
Length: 8
Type: Unsigned
Endian: Little
Multiplier: ???
Unit: ???

I have not quite deciphered the brake unit conversion yet. I have seen values of 0-120ish in practice. This is likely limited to just how hard I can press down on the pedal. This may be a position or pressure value.

Bump, anyone been able to get this setup via an OBD dongle? Would like to use this, if possible, with Harry's Lap Timer (HLT).

I never got this to work and those OBD signals I did get were out of sync and HLT tools for fixing this would a waste of time (circa 2018).

I gave up and bought a Aim Solo 2 DL.

Couldn't read the brake pressure via OBD, but at least was able to read pressed/released.
Better than nothing, at least should be possible to see braking points lap vs lap.

In RaceChrono, I use
0x7E0 for "OBD-II header"
PID 0x221233 for brake pressed/released (Mode 22, PID 0x1233?)
PID 0x22122F for clutch pressed/released
Equation: B / 2.55

Thanks @timurrrr, how are you obtaining these PIDs? Would be much easier to log them using Torque than pulling Tactrix at times...

I take brake pressure from CAN ID 209 (decimal), offset 2, length 1, unsigned, little endian. No equation needed. I think it's in Bar.

I believe you're reading it from CAN directly? Not from OBD-II, which is the topic of this thread.
How to read it from CAN has already been mentioned above.

Which device do you read it through? Can you send it to RaceChrono/HLT via Bluetooth?

I thought I would shed some light on the multiplier and unit. I'm using a RaceCapture Track MK2 which does PIDs and public CAN.
https://www.autosportlabs.com/produc...turetrack-mk2/

Just wanted to bring this up - the OBD Fusion app with the extended parameters has the brake pressure PID, which works well but the app is a little slow in responding. Would have preferred to port the PIDs to Torque which has much more flexibility, but at least there's the option for us FRS/86/BRZ owners.

Do they show which PID they use?

Also, which car did you test it on? FR-S, BRZ or [GT]86?
Those "extended parameters" are typically manufacturer-specific, and they consider Scion, Subaru and Toyota to be very different manufacturers.

I doubt it is different - I expect it to be universal across the models, given that the tunes for the 3 models are basically the same apart from some regional differences. For example my car is a JDM GT86 running a tune for Australian 86/BRZs with the OBD Fusion app set as a Scion FRS.

On getting the actual PID addresses and formula - unfortunately that's hidden away as getting those extended PIDs is a paid feature. You can only select it but not manipulate how it is calculated since it could be easily copied out.

On the other hand if we had someone able to do some RE we can probably make some progress...

That's what I was asking about :)

Anyhow, WE DID IT!
In RaceChrono format, the parameters are:
Channel: Brake Position (%)
OBD-II header: 0x7B0
PID: 0x2141
Equation: min(100, 1.1 * max(A-10, 0))

Explanation: the min/max trick makes sure the output is in the [0%, 100%] range. The 1.1x is a multiplier that roughly matches the scale factor I previously chose for my CAN bus reader so that 100% is reported when I'm braking really hard. The -10 offset is to compensate for the default value of 10 (I've no idea why the reported value never goes below 10).

Enjoy!

Having said that, OBD-II provides a much lower refresh rate than CAN, so I still recommend investing a little time into making a DIY CAN reader as documented on my GitHub:
https://github.com/timurrrr/RaceChronoDiyBleDevice

Nice!

To add on - the brake pressure PID visible in the app shows in two units: by MPa and by voltage. And in the voltage there is always a value (about 0.1v if I'm not mistaken) even when the brakes are untouched so it correlates back to your compensation. However the MPa value does go from 0 to 10 MPa - this is with me lead-footing the pedal :)

Would you have any insight on how to implement this on Harry's Lap Timer Custom PID Menu? The requested inputs are pretty different compared to what I've seen here and am used to.


Developer guide: http://www.gps-laptimer.com/LapTimer...%20Program.pdf



The input menu asks for

• Channel
  • Lists a bunch of available channels that HLT records to. Not particularly important, just the column in the default CSV that the application records to
  • I would map it to "Brake Pressure [kPA]" and scale it to % in post processing
• ECU
  • Defaults to "ALL" for functional calls
  • States to address a specific ECU if desired for physical calls (such as "ECM" or "TCM"), or when using custom mode $21, $22, $23 below
• Mode
  • Mode 1
  • Mode 9
  • Mode 21
  • Mode 22
  • Mode 23
• PID
  • 1, 2, or 3 byte hex strings
• Request Frequency
  • Low
  • Medium
  • High
• Formula
  • Basically C-language logic, similar to what was used in RaceChrono implementation

-------------------------

My best interpretation of the inputs that would work in HLT would be, with some feedback from the developer on a similar implementation [ http://forum.gps-laptimer.de/viewtopic.php?t=5589 ]:

• Channel: Brake Pressure [kPA]
• ECU:ECM
• Mode: Mode 21
• PID: 41
• Request Frequency: High (probably doesn't matter from a functionality point of view)
• Formula: =MIN(100 : (1.1 * MAX((A-10))))

Obviously, it doesn't have field to input a custom header like I'm used to seeing in applications like Torque (and RaceChrono). However, there is a way to specify a custom width for the parameter by adding leading zeroes. For example, specifying the PID as "41" allows it a width of 1 byte, but if we instead label it as 0041, it will be 2 bytes wide. Perhaps this is the way to incorporate the header?

Try ECU: 0x7B0.

If that doesn't work, you may want to ask on the HLT forum.
I know how to enter the config in RaceChrono and what underlying messages are sent over the bus, but never tried HLT, so don't know what format it wants for the OBD PID or ECU CAN ID.

Or you can try the superior CAN bus mode in RaceChrono :)