Civil Engineering Reference
In-Depth Information
together with ISO 15765-4/ISO 15031-5 for OBD communication. It is therefore
not enough to check the ParameterGroupNumber 61444 EEC1 to distinguish if the
vehicle utilizes SAE J1939-73.
The scan tool will build a list of the ElectronicControlUnits that has responded
to this request and the OBD compliance will be an input of the services that are
implemented. Table 1 of SAE J1939-73 states which DMs and which information
are needed to comply with different OBD legislations. It is not clear how to handle
smart sensors or smart actuators since these simple devices have a limited imple-
mentation of the diagnostic protocol. They have maybe only implemented DM1
active DTCs, DM11 clear DTCs, DM 19 CALibrationIDentification/Calibration-
VerificationNumber and DM5 for scan tool initialization, but the vehicle needs to
comply to FinalRegulationOrder 1971 which is for US10 legislation in California.
4.4.6
SAE J1939-81 81—NMT
SAE J1939-81 includes NMT, i.e. how to handle if two ECUs are connected to the
same network with the same ECU address. Normally two ECUs shall never share
the same SA, but in some type of vehicles, this may happen, e.g. a tractor with two
trailers with both trailers having a brake system.
It uses a NAME field and a method to claim addresses. If there are multiple
ECUs with same address, then the ECU with the lowest NAME will win and the
others have to claim other addresses. The claiming can be seen as an ECU address
arbitration. This works as the best in theory but there are problems in real life; the
ECUs detect bus-off before they could claim the address, they misunderstand the
response since maybe both ECUs respond to the same Name claim response and get
the same response, i.e. they cannot know if the data are intended for the own ECU
or the other ECU and both will react as for communication faults.
4.4.7
SAE J1939-84
The standard is a conformance test, but not equal to SAE J1699-3 for LDVs. The
J1699-3 is a conformance test for a complete vehicle and J1939-84 is a very thin test
specification for a single ECU. The implementation of the standard can also be down-
loaded as a Dynamic Link Library (DLL) on www.sourceforge.org. The standard is
used to verify that the application in the ECU fulfil the SAE J1939-73 standard.
4.5
CanKingdom
CanKingdom (CK), first published in 1990, is considered the ancestor of the CAN-
based higher layer protocols (HLP). In many respects, it is quite different from later
CAN HLPs:
