Truck & Off-Highway Engineering - August 2023 - 5

TECHNICAL INNOVATIONS
A technical session at the 2023 SAE
COMVEC event (https://comvec.sae.org/
program) will highlight developments in
diagnostics and prognostics for critical
vehicle electronic systems. Topics will
include the evolution of big-data techniques
to promote prognostic development
and case studies for zero-emission
and autonomous vehicles. Panelists are
expected from DG Technologies, RA
Consulting, Softing Automotive
Electronics, VHM Innovations and Volvo
Autonomous Solutions.
Diagnostic communication
Figure 1 shows a simplified but typical
setup of a diagnostic communication system.
It consists of the external test equipment
(TST), the Vehicle Communication
Interface (VCI) and the E/E system of the
vehicle. The E/E system consists of electronic
control units (ECUs) that are connected
via in-vehicle networks (IVN), but
also of sensors, actuators, wiring and connectors.
The VCI is connected to the E/E
system of the vehicle via a Diagnostic
Link Connector (DLC) as it is specified in
SAE 1962 or SAE J1939-13.
Diagnostic communication is characterized
by diagnostic service requests
that are sent by the tester to the vehicle
and diagnostic service responses sent
from the vehicle to the tester.
Figure 3:
UDS, OBDonUDS and
ZEVonUDS are based
on DoCAN / CAN.
Looking at a single temporal segment,
it is seen that the communication always
takes place between the single tester
and exactly one ECU (TST-to-ECU, ECUto-TST,
peer-to-peer). For a successful
communication, both TST and ECU must
support the same communication protocol
stack. As illustrated in Figure 2, a
protocol stack consists of seven layers
- for example, the Physical Layer (L1),
the Transport Layer (L4) and the
Application Layer (L7). Service requests
and responses are specified on Layer 7.
For the communication between external
test equipment - in this context
also referred to as " OBD Scan Tool " -
and the ECUs of the OBD system, legislative
authorities such as CARB and the
European Parliament / Commission
mandate the support of a standardized
diagnostic communication protocol
stack. In the near future, tool-based
diagnostics will include diagnostic communication
with an OBD system that
supervises the safety of the vehicle.
SAE J1979 and its " OBD Modes " have
been in use for decades, but due to regulatory
adoption of OBDonUDS, SAE J1979
now becomes a multiple-part document
series. SAE J1979-3 for zero-emission
propulsion systems defines ZEV as follows:
traction drive motors and their inverters;
energy storage systems; highvoltage
charging systems (including
components whose failures impact regenerative
braking); and thermal control
systems supporting propulsion (i.e., battery
cooling pumps and sensors).
Figure 3 illustrates that the OSI
Layers 1 thru 4 of the Application Layer
protocols ISO 14229-1 (UDS), SAE
J1979-2 (OBDonUDS) and SAE J1979-3
(ZEVonUDS) are the same: Diagnostics
on CAN (DoCAN). Optionally, ISO 14229
and SAE J1979-3 (and ISO 27145 =
World-Wide Harmonized OBD, or
WWH-OBD) allow the diagnostic communication
using DoIP and Ethernet.
Figure 4:
ISO 14229 (UDS)
Application Layer Services.
TRUCK & OFF-HIGHWAY ENGINEERING
August 2023 5
BOTH IMAGES: SOFTING
https://comvec.sae.org/program https://comvec.sae.org/program
Truck & Off-Highway Engineering - August 2023

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