OBD有标准的协议。可以参看ISO15031－5。但是还要看车辆，不同的车辆支持的参数是不一样的。
向OBD模块发送012F指令即为读取燃油量（需要车辆支持此参数）
OBD通讯协议
OBD-II Network Standards
» J1850 VPW
– Adopted by GM; also known as Class 2.
– Adopted by Chrysler (known as J1850).
– Some references to VPW mode heard about in regards to Toyota (and Honda ?).
– 10.4 kbps, single wire.
» J1850 PWM
– Adopted by Ford; also known as Standard Corporate Protocol (SCP).
– Also seen in some Mazda products.
– Some references to PWM mode heard about in regards to Mitsubishi.
– 41.6 kbps, two wire balanced signal.
» ISO 9141 and ISO 9141-2 (also known as ISO 9141 CARB)
– Seen in some Chrysler and Mazda products.
– Seems to be more common in Europe.
– 10.4 kbps, single wire.
OBDII 通讯协议
obdii generic communication protocols by manufacturer
Recently I tried to install my product on Peuzeot(406 or something
similar). There was
KWP 2000 bus. I tried to get the speed value from the bus by sending
the following string
0xc2 0x33 0xf1 0x01 0x0d 0xf4.
On responce I received two answers from 2 different ECUs:
1) 0x83 0xf1 0x10 0x7f 0x01 0x12 0x16
1) 0x83 0xf1 0xa4 0x41 0x0d 0x00 0x66
The first ECU sent me NACK
(This response code indicates that the requested action will not be
taken because the server (ECU) does not support the arguments of the
request message or the format of the argument bytes do not match the
prescribed format for the specified service.)
My question is: if there was something wrong with the arguments of the
request message, the second ECU also should not understand the
request, bit it did !
And the second question is: why the first ECU did send the negative
answer. If you look at the j1979 PDF you will find there that "If an
ECU does not support any of the PIDs requested it is not allowed to
send a negative response message".
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