Brake PID for M2 f87 og

SebLJ

Hello everyone, I share my discovery on braking PIDs for a BMW, M2 f87 engine N55

Channel: Brake Pedal Position (%)

PID: 0x 22 58 B7

Source data: 0x 00 00

Use live data: Enabled (toggle ON)

Equation:
(bytesToUint(raw, 0, 2) - 46848) * 100 / 138

Solution preview (with source data 0x0000):

Raw value = 0
(0 - 46848) × 100 / 138 = -33947% (expected at rest before pedal input )

MRRIZK

Are you sure this is correct?

0x58B7 - "aktueller Bremsdruck" transalted to english is "current brake pressure", and the value returned is hPa

SebLJ

MRRIZK You're right, but I wanted to have the percentage value, so I changed the equation 😅

MRRIZK

Ok, So that would imply that you know the range of the sensor to convert to a %. I will test it out.

BTW i have posted the gear position sensor calc in another thread that i think should work for you as well but mine is manual.

aol

One could convert a pressure value to %, by using the "min(a, b)" function to add 100% ceiling. Then use slightly bigger multiplier, so lower pressure is interpreted as 100%. The pressure value is useful in analysis, but the percentage value is very nice for video overlay.

MRRIZK

@SebLJ What I noticed in my testing was a few things:

The max pressure observed is lower with each repetitive depress of the brake pedal. If you let it sit for a bit, then the recorded pressure is higher. I'm suspecting that this ties into the BMW's brake assist where it tries to make it feel the same for the driver for repetitive execution in a short period of time. There are a few threads on bimmerpost for people coding this out I believe.
I suspect this PID is not true pressure but a calculated pressure of some sort. Testing with BM3 they have a RAM Channel (not obd) for brake pressure that reads consistently from 0-90 Bar and does not appear to change with repetitive depresses.
My delta between reading at rest vs fully depressed maxed out about 109

Below is my adjusted formula taking into @aol suggestion (i think) with the min/max. Seems to work for me and would pair well with linear gauges for brake and throttle. Wink Wink..

int(min(max((bytesToUint(raw, 0, 2) - 46848) * 100.0 / 109, 0), 100))

aol

MRRIZK Just programmed a horizontal bar gauge yesterday. I'm not sure if people will like it, but it's a start. I tried to make it look good 🙂 Will be in the next version.