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Volt Features
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 , 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 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

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.


Martin from British Columbia

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