MACS Monthly Newsletter - 2022 - APR2

Chevrolet Volt Hybrid/EV Electronics coolant pump.
Verifying the wiring and control signals using both a
DVOM and a lab scope applies in this example.
Coolant
As mentioned earlier, it is probable that Hybrid
and EVs will be on the road longer than their ICE
counterparts. Severe climates demand even more
from coolant.
Coolant service is imperative for Hybrid and EVs.
Following the manufacturer's maintenance schedule
(at the very minimum) will decrease the likelihood of
high voltage cooling systems developing issues.
High voltage cooling system failures are very simiFigure
2: 2008 Toyota Prius battery blade air gap.
Intermittent coolant pump failures have started to
present themselves in many areas. I am not a fan of
using the Diagnostic Dart Board. If you or your diagnostic
equipment could use updating, it 's time to get
up to speed. A lab scope has become an essential
tool for any shop serious about diagnosing and repairing
vehicles. Depending on your shop's business
model, you may not need a top-line Snap-On or Pico
kit, but you should at least have a scope to investigate
two or four waveforms on the same screen.
Diagnosing something as simple as a coolant
pump is sometimes best accomplished using a lab
scope. Figure 1 illustrates the complexity of a 2016
High voltage isolation
Hybrid and Electric Vehicles (EVs) use two separate
electric systems to operate. The 12-volt system
operates independently of the HV System. They do
not even share chassis ground...or are " Isolated "
from each other. Put another way, using conventional
theory, every electron leaving the HV Battery Positive
terminal is expected to return to the HV Battery
Negative terminal through a dedicated ground wire
which is NOT connected to the chassis.
The " classic " 12-volt system we are already familiar
with is used to control every ECM and accessory
on the vehicle. When the vehicle is off, these
modules go to sleep, networks shut down and a very
slight parasitic battery draw is present to maintain
memory. Unlock the doors with the remote, press the
start button or turn the key and the 12-volt system
comes to life. ECM-controlled systems and creature
comforts are initialized, perform their self-test and
are ready to go almost instantly.
The HV system performs the same test on itself.
Before the High Voltage system is engaged, just
like every other system on the vehicle, a self-test is
performed. The system also checks for " phantom "
draw. If everything checks out, the main contactor
is closed and High Voltage from the traction battery
is available to all HV components.
Figure 3: 2008 Toyota Prius High Voltage battery and
cooling system.
April 2022
2
Current flow and HV wire resistance to HV Battery
Ground is also constantly monitored. Any " leakage "
MACS Service Reports
lar to ICE cooling system failures. Leaking radiators,
leaking reservoirs, failed pumps, collision, hose failures,
abrasion, component leaks, component corrosion.
There is one failure unique to HV cooling...
High Voltage Isolation Codes caused by the cooling
system.
Mike Bailey
Mike Bailey
MACS Monthly Newsletter - 2022

Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2022
