October 2022 - 22

somewhat opposing signals, which are used to validate proper system
operation. The DBW system took on a lot of heavy risk assessment
study and had to pass through the Automotive Safety Integrity
Level (ASIL) steps before standards for design and implementation
could be approved. Generally, these systems have provided vehicle
manufacturers additional tools that can be used to enhance vehicle
performance, achieve emission compliance, minimize drivetrain
wear, and maintain overall safe vehicle operation.
SCOPING THE PROBLEM
Service technicians dealing with intermittent faults on such
systems should be aware that the safety engineers, as per safety
requirements, must deploy a series of safety checks on the TAC
systems before any propulsion torque commands can be issued
to the vehicle. What this means is that upon key up or vehicle
wake up, the system will run routines designed to validate the
integrity of the system. The state of health checks may include
RAM/ROM/EEPROM tests, analog-to-digital conversion tests,
mechanical performance tests, shutdown tests, and so on. When
a technician is dealing with a suspect throttle body, they may
consider taking a deeper look at the throttle body using a digital
storage oscilloscope (DSO), such as shown in Figure 2.
Techs interested in seeing a self-test in operation can use their
DSO to analyze this. Two channels can be used to log both throttle
position sensors, and an amp current probe can be used on one of the
motor circuits. The image shown in Figure 2 is from a 2004 GM V8
application, which was setting a P0120 (TP1 Circuit) and a P2135
(TP 1-2 Signal Correlation). The time shown between the cursors
equals 486ms, which was captured at key up.
Figure 3 zooms in to the first 26ms of activity, where I observed
what appeared to likely be a mechanical interference condition of the
throttle plate, which was affecting both TP signals. The throttle body
was extremely coked up with carbon and since it had over 200,000
miles on it, we recommended replacement over cleaning.
After replacement of the throttle body, I proceeded to collect
a comparison DSO trace, so I could see what a new, known-good
throttle body would look like during the same key-up self-test. Figure
4 shows a properly operating system.
I have collected dozens of images like this and have seen some
that helped me to identify high commutator resistance on a brushed
DC motor that I could not get to exhibit the symptoms described by
the vehicle owner to appear while it was in the shop. However, the
scope was able to provide me with some additional data points I then
used to reinforce my recommendations for component replacement.
BRAKING SYSTEMS
With the introduction of anti-lock braking (ABS), we've seen
quite a few new pieces of hardware occupy the vehicle. Today,
we're seeing more and more alternative propulsion systems, such
as hybrids and battery electric vehicles (BEVs) populating the
fleet. With this new technology comes significant changes with
the operational characteristics of the vehicle, often demanding
other vehicle control methods.
Since hybrid and battery electric vehicles can take advantage of
converting vehicle kinetic energy into electrical energy, additional
engineering produced methods to reduce speed without much
expense in brake wear. Therefore, you tend to see less brake wear
on such vehicles if the vehicle is being operated properly.
RELATED PRODUCTS
Electronic Specialties
Super Relay Buddy, No. 194
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Pico Technology
PicoScope,
Power Probe Group
Volt Tester,
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on VehicleServicePros.com
No. VT750LCD
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22 PTEN OCTOBER 2022 www.VehicleServicePros.com
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October 2022

Table of Contents for the Digital Edition of October 2022
