october2023 - 48

DIAGNOSTIC TECH
With the vehicle powered off (sometimes requiring
a battery disconnect) a DVOM can be deployed to begin
interrogating of the network connectivity by assessing terminating
resistance. However, this is highly dependent on
network wiring. In most cases, the technician can assess
network wiring integrity and then begin performing connector
integrity (wiggle) testing but only after they have a
solid understanding of the wiring and termination strategy.
But you may ask, how do I verify the integrity of the other
modules on the network, and can I leverage the fact that
there is a 2.7k ohm in the other modules? With the ECM
disconnected and measuring the resistance between CANH
and CANL, your measurement would reflect the entire parallel
resistance of the circuit. The number of modules on the
circuit would dictate the value however, with the meter in
sight, one could start wiggling suspect connectors looking
for a change in resistance. Another test to perform is the
resistance test from CANH and CANL to ground and B+.
Obviously, either of those with continuity would result in
a major network failure.
Mini-Ductor® Venom®
On the VW example, all connections were found to be
problem-free and after clearing all the DTCs and road testing
the vehicle on several occasions over the course of a couple
of days, the problem resurfaced which occurred right after
startup. Not all the previously reported DTCs were set but
enough information was gathered which pointed to a module
fault. In this case, it was the brake control module that was
suspected to be at fault in the beginning.
U0235 CASE STUDY
Recently, one of my apprentices informed me that his friend's
2019 Toyota Tacoma was exhibiting an error message on the
cluster stating that the pre-collision system was disabled and
a U0235 was stored. This seemed to surface after they were
using a scan tool on the vehicle at school. After performing
some research, we discovered that this code was set when
they entered test mode and then immediately exited that
mode. Toyota's service information provides more detail as
to why this is.
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48 Professional Distributor I October 2023 I VehicleServicePros.com9/6/23 4:10 PM
O2 SENSORS
TOOLS FOR TESTING
DVOM: We've already discussed leveraging the power of the
ohmmeter for testing but what about using the voltmeter or the
scope? The voltmeter can serve a purpose by measuring CANH
and CANL referenced to the ground. Since the non-dominant
voltage level for each ride is at 2.5V, depending on how much
traffic (bus load) there is the CANH will measure slightly
higher than 2.5V and the CANL will measure slightly lower.
Scope: While the scope is a powerful tool, it must be
used with caution since it can take the technician down the
wrong pathway if he or she doesn't know what to expect. An
example of this is shown in Figure 6 where normal message
arbitration is taking place. It's entirely possible that a
technician seeing this for the first time may begin to suspect
that this is an anomaly and decide to research further. The
higher levels shown are simply because at least three different
modules started to communicate their message IDs (during
the arbitration period) with one (or more) dropping off at the
next bit until the message with the lowest ID won and was
then able to continue to broadcast its message (Figure 8).
Sniffers: CANBUS sniffers may also provide support
for network troubleshooting as they can provide additional
information such as bus traffic (load) and other statistical
data such as the number of errors and other data metrics
(see Figures 3 and 4). Knowing the bus load could prove
to be helpful in cases where aftermarket devices have been
unknowingly added to the network and may be the source of
the problems you're researching. One that I've been using is
CANCapture from eControls as mentioned earlier. Another
tool is the PhysiCAN SnS GRIP Tester from Sital which
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october2023

Table of Contents for the Digital Edition of october2023
