问题
I working on an app that I need to calculate distance travelled from point A to point B (by car).
I asked Elm Electronics (chipset manufacturer) and they said there is no standard OBD-II PID to return mileage from odometer, although car manufacturers might provide a PID. Since this way is not standard then I found another way.
PID 0131 (Distance traveled since codes cleared), is returning something that I think might be helpful. IF i'm able to clear it at point A and read its value at point B then I'm done :)
I thought a lot to guess what does "codes cleared" mean but I couldn't realize what does it mean? and my another important question, how to clear code or reset this PID?
Any suggestion would be appreciated. Thanks.
Update
I just tested on two Cars.
- On Benz car no OBD-II command works. I couldn't get any data :(
- I got correct reply on Persona car (Local Malaysia) but 0x0131 PID was always returned 7F01 which is 16608KM even after passing few Kms. I tried to reset it by sending 04 command (as Eric suggested on his answer), However, nothing got clear :) and I still got 7F01 as response.
My Library can be used for anyone who is looking for OBD-II lib from here.
So, What I plan to do is, since I'm able to get speed (v) then I'm able to calculate distance based on d = v * t formula.
回答1:
Elm Electronics are right. The resetting trouble codes solution is a possible, but maybe unwanted workaround though.
Mode 04 is for resetting the codes. Sending 04 will reset the MIL (Malfunction Indicator Light) and reset the codes you want to reset.
In the comments, Chris suggested to use the value, and than keep track of this value yourself. That way you don't need to misuse the Mode 04. Th 0131 value overflows at 65535 km. But when you bring you car in for maintenance, they could reset this value, depending on who is maintaining your car ofcourse.
Source: Mode 04 - Wikipedia
回答2:
There are two PIds: 0x0121 Distance travelled with malfunction indicator lamp (MIL) on which keeps the distance with MIL on and 0x0131 Distance travelled since codes cleared which keeps the distance after clearing the MIL by using mode 0x04. By saying code, it meant the Diagnostics Trouble Code (DTC). When one of them keeps counting the distance the other one is fixed and activation is done for them only based on MIL on or off.
For having the milage, afaik, you need to have current mileage from the odometer as the reference, in addition to those two PIDs. For example, if the current mileage on the odometer* is X and the first time readings for those two PIDs are Y and Z respectively, and x and y are real-time readings from those two PIDs, these two formulas can give you the mileage and trip distance:
Real-Time mileage** = X + (y - Y) + (z - Z)
Trip distance (MIL Off) = x(end) - x(start)
Trip distance (MIL On) = y(end) - y(start)
*The odometer is supposed to be available by PID 0x01A6 Odometer, but in almost all the vehicles, it's not supported.
**The overflow in readings from those two PIDs should be considered as well.
回答3:
I think You can use the PID 0x011F (Run time since engine start) and PID 0x010D (Vehicle speed). If you save these values in an sd card then you can multiply these two values.
来源：https://stackoverflow.com/questions/27736828/android-obd-ii-how-to-clear-distance-travelled-pid0131