october2022 - 36

DIAGNOSTIC TECH
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.
On the internal combustion engine
Figure 5 - The GEN 2 iBooster from Bosch
(ICE) side of the propulsion systems found
on hybrids and extended range vehicles,
engine vacuum was no longer abundantly
available to supply the traditional power
brake booster. This required either the
addition of an electric vacuum pump or a
complete redesign of the braking system.
Looking back at the Toyota Prius, they
relied on an electric pump to multiply the
braking force applied to the brake pedal
using a hydraulic pump and accumulator
and in-turn, had to deploy a stroke simulator
to provide the proper pedal feedback
to the driver.
As the driver increases pedal force,
Figure 6 - The iBooster provides the power assist through its internal brushless DC motor
elevated pressurized brake fluid is applied
to all four-wheels programmatically
(other manufacturers may deploy different
methods for brake assist). When
working on these systems, one should
36 Professional Distributor I October 2022 I VehicleServicePros.com
http://www.VehicleServicePros.com
october2022

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