Accessing vehicle Wheel Speed
Discussion
Not sure if this belongs in a different section, however, is it possible to easily access the wheel speed data over the ODBII bus? I've googled a few different terms, but mainly get results about wheel speed sensor faults. Most ODBII readers I have found are fault code readers which isn't what I need.
I just want to be able to access the wheel speed over CAN, do a bit of data reformatting, and output again to another system. I really don't want to have to fit a separate wheel speed sensor for the work I'm doing. I thought about using precision GPS, but that can get noisy at low speeds.
I just want to be able to access the wheel speed over CAN, do a bit of data reformatting, and output again to another system. I really don't want to have to fit a separate wheel speed sensor for the work I'm doing. I thought about using precision GPS, but that can get noisy at low speeds.
The standardised diagnostics are just a bit of a bare minimum of basic fault codes, mostly emission-related.
There will be much more information available, but it'll be buried in manufacturer-specific protocols. You might be able to get the individual wheel speeds, but it'll depend on the car, and you'll probably need either a dealer box or something close in capability.
There will be much more information available, but it'll be buried in manufacturer-specific protocols. You might be able to get the individual wheel speeds, but it'll depend on the car, and you'll probably need either a dealer box or something close in capability.
J1962 OBD includes vehicle speed as one of the standard Parameter IDs (PIDs) it's 0x0D, and is in kph, with 8b resolution between 0 and 255kph (ie a resolution of 1kph)
This value will usually be a filtered average of the 4 true wheelspeeds from the ABS controller, although on older cars it can be the derived from gearbox output shaft speed read by the Dash Display.
Of course, assuming you have a suitable CAN interface, it will be very easy to find the none J1962 vehicle speed CAN message on the powertrain bus, which will probably be a 16b value with 0.125kph resolution or better
This value will usually be a filtered average of the 4 true wheelspeeds from the ABS controller, although on older cars it can be the derived from gearbox output shaft speed read by the Dash Display.
Of course, assuming you have a suitable CAN interface, it will be very easy to find the none J1962 vehicle speed CAN message on the powertrain bus, which will probably be a 16b value with 0.125kph resolution or better
What vehicle or vehicles and what kit do you have?
Do you need individual wheel speeds or an overall speed?
You can try to reverse engineer the information from the raw CAN data. As said above, usually 2 bytes and one of the higher priority messages.
Alternatively if you have a diagnostic tool you can "sniff" the diagnostic request and response, then use that, albeit usually at a slower update rate.
Do you need individual wheel speeds or an overall speed?
You can try to reverse engineer the information from the raw CAN data. As said above, usually 2 bytes and one of the higher priority messages.
Alternatively if you have a diagnostic tool you can "sniff" the diagnostic request and response, then use that, albeit usually at a slower update rate.
Thanks for the replies. I think a 2Byte message would be useable, 1Byte wouldn't be accurate enough. I've got access to a 2011 Defender, and a 2013 Focus.
Thought I'd made a miracle breakthrough when someone pointed out we have a Kistler sensor. No idea why we have it, but unfortunately it is not road legal.
Thought I'd made a miracle breakthrough when someone pointed out we have a Kistler sensor. No idea why we have it, but unfortunately it is not road legal.
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