User's Guide

Setup
From the Web Interface, check the "Start OBD2ECU" box, and select CAN3 from the dropdown
menu (if using the wiring diagram above). This will enable the OBDII ECU Task to run the next
time the OVMSv3 module is powered on or reset. Also check the "Power on external 12V" box
in order to feed 12v power through to the device. Click on Save at the bottom of the page.
From the command line, the following commands are available
obdii ecu start can3 Starts the OBDII ECU task.
obdii ecu stop Stops the OBDII ECU task
obdii ecu list Displays the parameters being served, and their current value
obdii ecu reload Reloads the map of parameters, after a config change
power ext12v on Turns on power feed to the device
power ext12v off Turns off power feed to the device
Operation
During operation, an OBDII device, for example, a Head-Up Display (HUD) or OBDII Diagnostic
module, will make periodic requests, usually a few times per second, for a set of parameters.
The OVMSv3 module will reply to those parameters with the metric if configured to do so, on an
individual basis. These parameters can be common items such as vehicle speed, engine RPM,
and engine coolant temperature, but because of the differences between ICE and EV vehicles,
many of the parameters do not have equivalent values in an EV. Speed and engine (motor)
RPM can be directly mapped, but there is typically no "engine coolant". That parameter (in fact,
most parameters) can be mapped to some other value of interest. For example, the Engine
Coolant display on the HUD can be configured to display motor or battery temperature instead.
Engine Load (PID 4, a percentage value), is mapped by default to battery State of Charge (also
a percentage). However, note that not all vehicle metrics may be supported by all vehicles.
Parameters requested by the OBDII device are referred to by "PID value". Note that each PID
has a specific range of allowed values, and that it is not possible to directly represent values
outside that range. For example, PID 5 (Engine coolant temperature) has a range of -40 to
+215; it would not be possible to map the full range of motor RPMs to this parameter. Values
outside the allowed range are limited to the range boundary value. The complete table of
possible parameters are described here: https://en.wikipedia.org/wiki/OBD-II_PIDs#Mode_01
Vehicle metrics are referred to by name. See the table in Appendix 1 for a list of available
metrics, which vehicles report them, and which of those are of a format that can be mapped by
the OBDII ECU task.
OVMS v3 User Guide Page 74 / 86