October 2023 - 40

p Figure 8 - U0235 Warning, Toyota Tacoma
Photo from Toyota TIS
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.
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,
I N N O V A T I N G
SAFETY
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. See Figures 8 and 9.
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
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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 10).
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October 2023

Table of Contents for the Digital Edition of October 2023
