Description / Abstract:
Purpose - This SAE Recommended Practice supersedes SAE J1978 FEB1998,
and is technically equivalent
to ISO/DIS 15031-4:December 14, 2001.
This document is intended to satisfy the requirements of an OBD scan
tool as required by U.S.
On-Board Diagnostic (OBD) regulations.
The document specifies:
a. A means of establishing communications between an OBD-equipped
vehicle and external test
equipment,
b. A set of diagnostic services to be provided by the external test
equipment in order to exercise
the services defined in SAE J1979,
c. Conformance criteria for the external test equipment.
Differences from ISO Document - The ISO 15031-4 document is intended
to satisfy the requirements of
OBD requirements in countries other than the U.S., and includes
functionality not required or not
allowed in the U.S.
Notable exceptions are:
a. Proposed U.S. OBD regulations will allow ISO 15765-4 as an
allowable OBD serial data link at 500
kbps only. Only those provisions of ISO 15765-4 that pertain to 500
kbps are required to be
supported by an SAE J1978 diagnostic scan tool.
b. Proposed U.S. OBD regulations will not allow greater than 20 V at
the SAE J1962 connector. Only
the Type A connector as defined in SAE J1962 needs to be supported by
an SAE J1978 diagnostic scan
tool.
Differences between the documents are highlighted in the technical
requirements sections of this
document. Deleted text is highlighted with struck through and new text
is highlighted with bold
italic.
NOTE - To maintain equivalency of the documents, a comma is used as a
decimal marker for numeric
values in this document.