Posted to Technical Theory Forum on 12/5/2011
11 Replies
Recently, I had the opportunity to audit a Chevrolet Volt
battery diagnosis and safety course. Since I always have a
camera handy, I snapped a few photos along the way and have
posted them here for your interest. My aim is to show you
some of the stuff that isn't shown in the fancy photos taken
from a distance and provide a few details.
This post is intended only as an introductory FYI topic of
interest to describe a few of the electrical features as
they relate to battery safety and diagnosis. See the service
manual for in-depth step by step procedures and always
follow Personal Protective Equipment and tool requirements
and observe all safety precautions and labels.
Since the vehicle has been available in USA as a 2011 model
and more recently in Canada as the 2012 model, if you ante
up for a short term subscription to GM electronic service
information at www.acdelcotechconnect.com , you can read up on how the
various systems function and learn about the diagnostic
procedures and system tests. Rely on the expertise of GM
dealer technicians for their encounters with this vehicle,
James Avery in particular having posted some useful and
interesting case studies to date on programming issues.
Sorry if others have posted some good stuff, that I have
missed.
With the technological advances being made daily, there's
not a lot of room for "nuts and bolts" only technicians
these days, so if you're the slightest bit intimidated by
technology, its probably a good time to consider your next
career move, before it is mapped out for you by someone
else. If you're not faint-hearted, embrace the technology
and climb aboard as the future that Jim Wilson and others
warned you about is here and already marching on to bigger
and greater things. All manufacturers have advanced
technologies that are demanding high levels of diagnostic
expertise. If you're not interested you might as well give
up now or make plans.
As with any electric vehicle or hybrid system, when
servicing specific components or areas of the vehicle, it is
necessary to disable the high voltage energy storage system.
The methods and needs vary from one vehicle to another,
depending on the area of service. Refer to GM SI document
#2409469 for the complete description of disabling and
re-enabling the high voltage system and observe all warnings
and caution labels.
There are many links to Volt First Responder Guides as
posted on the GM Service Technical College website can be
stumbled upon by doing a simple search. Here is one result
http://www.evsafetytraining.org/resources/auto-manufacturer-resources/~/media/Files/PDFs/VoltRespondersGuide.pdf that provides some nice photos
and general descriptions of the component locations within
the vehicle. My photos will provide a little closer look at
actual connections and some of the key components. Refer to
service information for actual or complete procedures.
Here is a photo of the Manual Disconnect Plug, identifying
the main and charger interlock circuits to the front and
rear of the plug, respectively. [2012 Chevrolet Volt,
BATT/Charging/Starting Photo]
A pair of jumper harnesses are required to make connections
for testing at the Battery Junction Block under the vehicle
at the front of the battery pack.
[2012 Chevrolet Volt, BATT/Charging/Starting Photo]
Here's a "fuzzy" photo of the under car access once the
exhaust and heat shield has been removed. Not shown is the
rear of the cradle that borders the photo and restricts ease
of access. [2012 Chevrolet Volt, BATT/Charging/Starting
Photo]
Set up a Fluke 87V and test the leads for continuity, must
read < 1 ohm resistance for each wire and not be shorted
together. These jumper leads will be connected directly to
high voltage connectors X4 and X5 under the vehicle once the
vehicle harnesses have been disconnected from the junction
block, since access is somewhat restricted at the front of
the battery pack.
Accessing the junction block requires the front exhaust pipe
to be disconnected from the manifold and hanger, O2 sensor
disconnected then the exhaust moved to the left side of the
vehicle and tied in place. After removal of the heat shield,
the junction block with its myriad of connectors can be
accessed reasonably well, although my interpretation of
"reasonably" may differ from yours! Let's just say that you
can accomplish the tests at the junction block without
bodily injury, but there's only room for one person.
[2012 Chevrolet Volt, BATT/Charging/Starting Photo]
Following the sequence for connector removal, note that for
each high voltage connector latch access, a smaller
interlock connector placed directly in front of the high
voltage latches, must first be removed. See photo for
description of the TPA security system. [2012 Chevrolet
Volt, BATT/Charging/Starting Photo]
With the integrity of the jumper test harnesses verified and
installed, perform voltage tests at each terminal of the
harnesses to ground and from each pair of harness terminals
to one another. This will confirm that the contactors are
open and not allowing any energy from the high voltage
battery to reach the junction block. Continue testing at the
vehicle harness side of the connectors and repeat the same
tests.
Without switching the meter off or changing functions,
verify the DMM still reads voltage of a 12 volt battery. A
9v battery is a suitable substitute. Once it has been
established that the voltage measurement was within the
desired specifications, the vehicle is considered to be
safe. However, always consider that there may be times
during diagnostics when the technician must "glove up"
again, along with following other PPE, clothing and footwear
requirements and recommendations.
The above checks and complete sequence isn't any more
difficult than for other electric or hybrid vehicles. When
disabling the systems all the way back to the high voltage
battery. If you are comfortable working on hybrid vehicles,
you likely won't be intimidated by similar procedures for
disabling and re-enabling a Volt high voltage system.
There are some more unique procedures involved with
servicing of the battery pack, including the requisite
support fixture to which the battery must be secured, prior
to removal. The intent is for the battery to become a
serviceable rather than replacement assembly and SI lists
various procedures for replacement of battery sections, when
a battery has a failure. Since the batteries are liquid
cooled, a pressure test must be completed during any service
where the battery sections or junction block have been
disconnected.
The Volt battery pack, along with various interface modules,
BECM, contactor assembly etc., are mounted on a carrier
inside a sealed housing. During manufacture, the assembly is
helium filled to reduce the possibility of moisture
contamination. When the cover housing is removed, the butyl
seal must be inspected and after reassembly, the unit must
be nitrogen and smoke tested. The vents are to be covered
with duct tape and the nitrogen evaporative emissions test
cart used in conjunction with the 0.040" leak test adaptor,
to pressurize the housing for leak testing. Here is a closer
look at several vents on a sheet made from Gore, essentially
the same stuff as Goretex clothing [2012 Chevrolet Volt,
BATT/Charging/Starting Photo]
A Battery Leak Tester EL 50512 is supplied though Kent Moore
Tools, to cap each of the Battery Junction Block electrical
connector cavities. [2012 Chevrolet Volt,
BATT/Charging/Starting Photo] Here is one of the connector
plugs used for leak testing [2012 Chevrolet Volt,
BATT/Charging/Starting Photo]
When the assembly is under pressure as noted by slight
bulging of the duct tape at the vent locations, the system
can be checked in the same way that nitrogen is used on
other systems, with the light. Switching to smoke,
similarly, leak tests can be completed. At the end of the
test, the vent material is replaced with Gore patches. Here
is a view of the T6 Power Inverter Module and the various
electrical connections [2012 Chevrolet Volt,
BATT/Charging/Starting Photo]
Here is a photos of the rear view of the Junction block that
mounts to the front of the A4 Rechargeable Energy Storage
System (RESS) battery pack. [2012 Chevrolet Volt,
BATT/Charging/Starting Photo] , showing various
electronics and the cooling system temperature sensor
locations at inlet and outlets.
Mounted to the rear of the Junction Block is a housing
[2012 Chevrolet Volt, BATT/Charging/Starting Photo]
containing the A28 contactors and pre-charge resistors and
also the Battery Energy Control Module that receives
information from four Interface Modules (one on each Section
1 and 2 battery and 2 for section 3).
We have looked at only a few of the features of the
electrical system as they relate to battery and power
management. The portable 115 volt charger is also worthy of
mention [2012 Chevrolet Volt, BATT/Charging/Starting
Photo].
GM SI document # 2676040 and the vehicle owner's manual
describes how this functions and what the various possible
illumination combinations of charging level and status
indicator lamps signify, in conjunction with an indicator
mounted on top of the dashboard at the base of the
windshield. The charger can be configured to charge
immediately, delayed or timer start and more, including
being able to change your mind on whether immediate or
delayed charging can selected, by a simple re-plugging
sequence. With self-diagnostics built in to the unit, it
ain't no ordinary extension cord. Another cord by "Coulomb"
is said to have some issues at this time, that GM is working
to fix with software. Personally, I would have expected the
cord manufacturer to make it function on the vehicle, rather
than the vehicle manufacturer working to accommodate a
different cord, but I don't have much info, so it is hearsay
at best. Let's just say that all cords are not equal, so
buyer beware. If you need to replace a charging cord, it
currently requires a TAC case and dealer BAC code, as we
experienced when a cord received some mild insulation damage
recently. There are plenty available in Flint Michigan, but
procuring a replacement requires some dialogue and approval
on this side of the border.
Note: If the 12 volt auxiliary battery requires charging,
that must be accomplished using a conventional charger
connected directly at the battery in the trunk. The 115 volt
system does not automatically charge the 12 volt battery.
The 115 volt cordset is designed to be used in conjunction
with a dedicated minimum 15 amp receptacle. However, in
instances where that may not be possible, the system can be
set to charge at a reduced rate of 8 amps if need be.
As far as the general battery assembly, there are three
sections, 1, 2 and 3. 1 and 2 are longitudinally mounted and
section 3 is mounted transversely. The 3 sections comprise 9
modules. The battery has a total of 288 cells. Cells are
assembled in groups of 3 and known as "Triplets". 288 cells
= 96 Triplets and the battery PID is displayed in GDS to
reflect this number of batteries, along with BECM reported
voltage values.
Battery Section 1 is at the front, behind the Junction
Block, Contactors and BECM. It contains 30 Triplets
identified as batteries 67-96 (modules 7, 8 & 9).
Battery Section 2 is directly behind Section 1 and contains
24 Triplets, batteries 43-66 (modules 5 & 6). Section 3
contains 42 Triplets, batteries 1-42 (modules 1, 2, 3 &
4) Information lists 16 thermistors and 4 Interface modules
connected to and mounted to the battery assembly. When
removed, the Manual Disconnect Plug disconnects battery
sections 2 and 3.
There was of course, much more to the course, including the
various vehicle operating modes, battery parameters and
diagnostic activities, but unless the vehicle is readily
available to follow the diagnostic sequences its best left
for another time.
Hopefully, this brief glimpse gives you a little insight
into the layout of the Volt main electrical system
connections. There are plenty or websites linking to
information about the battery and Electric Drive Unit (aka
transaxle) and the operating modes.
Googling "Volt Deep Dive" for bootleg videos captured by
media during GM engineer Pamela Fletcher's presentation,
will net this video containing Volt Deep Dive Parts 1, 2 and
3 http://www.youtube.com/watch?v=d9-9atMw6Zs
There's a lot of "mythconception" and "mythunderstanding"
about this vehicle, mostly put forth by the media to
sensationalize the effects of accidents and other conditions
that would result in more severe and dramatic scenarios in
gasoline only powered vehicles. Many in our own "circles"
have uninformed opinions or preconceived notions based on
make believe and supposition. So, whether you like or
dislike the Volt and vehicles in the pipeline employing
similar technologies, I recommend that you don't trash
products based on you own lack of knowledge and expertise.
Vehicles of this type are here now and they are not going
away any time soon in the new "real world" of automotive
service and repair.
There is a lot that we do not know about in complete detail
at this point in time and also the possibility of other
vehicles built on the Voltec platform as I have seen in
photos. I look forward to auditing more courses as they are
introduced, as the technology within this vehicle is
extremely interesting. Hopefully, as GM technicians dealing
with the vehicles in the dealership service bays encounter
interesting issues worthy of case studies, we can all learn
more from their experiences. It's still just another
vehicle, but there are technical innovations and
developments that are both very interesting and challenging,
depending on your perspective.
Regards,
Martin from British Columbia