By Jason Emery
From the 2008 vehicle extrication e-Newsletter, sponsored by
This spring, General Motors (GM) released its new GMC Yukon and Chevy Tahoe hybrids. For GM, this marks their entrance into the “full hybrid” market, joining Toyota, Ford, Nissan, and Lexus. A full hybrid vehicle can move at low speeds using only the electric motor; at higher speeds it may be powered by both the electric motor and the gasoline engine. Some of the features found in this new model are described below.
Vehicle Identification
At first glance, the vehicle’s physical build is no different than that of the nonhybrid version. However, special badging indicates that it is a hybrid. The emblems are located on the lower right corner of the vehicle’s liftgate (photo 1) and on the driver- and passenger-side C posts (photo 2). They may also appear on the front fenders. Additionally, if the eighth digit of the vehicle identification number (VIN) is a 5, then it is a hybrid. The vehicle’s dashboard markings also provide a solid identification method to determine if it is a hybrid. If the tachometer has an Autostop indicator (photo 3) and an economy gauge (photo 4), you know you are dealing with a hybrid. Additional indicators found under the hood include the hybrid logo and a high-voltage warning label on the plastic engine cowling (photo 5).
Hybrid Systems and Operation
This vehicle operates on a 300-volt high-voltage (both alternating (AC) and direct (DC) current) full-hybrid system (termed “Two-Mode” by GM). As with other hybrids, battery charging is accomplished through regenerative braking as well as through using power from the gasoline engine. The vehicle can operate at speeds up to 25 mph with the electric motor alone, depending on the acceleration demands placed on the vehicle. The Electric Power Steering (EPS) operates off a stepped-down, 42-volt system. A 110-volt AC outlet is also provided in the left-rear corner of the cargo area. Orange wiring indicates high-voltage and blue wiring indicates medium- or intermediate-voltage wiring. The 300-volt battery is located under the second row seat.
Response Considerations
Controlling Hazards
Never approach any vehicle involved in an accident from the front or the rear; always approach from the side. This is especially important for hybrid vehicles in which the engine may appear to be off, but could simply be in its “ready” mode. This would allow it to move with no warning if the driver were to take his foot off the brake or inadvertently hit the accelerator. Secure the possible movement of the vehicle by placing it into park and engaging the parking brake if possible. Chocking the wheels to prevent movement is a viable option if the damage to the vehicle prevents the above-mentioned options.
Once the unexpected movement hazard is addressed, it is time to control the high-voltage and occupant-protection systems. There are two methods. The first option is to turn the ignition off and disconnect the positive cable from the 12-volt battery (as indicated in the vehicle’s ERG). If you are unable to access the ignition, disconnect the positive cable from the 12-volt battery, then cut all three exposed 12-volt positive cables. The cut points have been marked with yellow tags (photo 6). Although removing the positive cable is differs from the customary method of disconnecting the negative side, the ERG recommends this method because of how the system is wired.
In addition, this vehicle has a service-disconnect lever to disconnect the high-voltage battery from the rest of the system. It can be accessed via the passenger side rear door and by lifting up the second row seat (photo 7). Under the seat is a piece of plastic that needs to be removed to access the lever. Once the lever is accessed, simply pull up, then down towards you, and then straight out (photo 8).
Even after using these shutdown procedures, it is still recommended that you assume that the entire high-voltage system is still energized. At a minimum, the battery will still remain energized after the shutdown procedure is completed. If the battery is damaged or exposed, do not attempt to access and the service-disconnect lever. In such a scenario, only a trained technician should attempt to do so.
Extrication Operations
As with all hybrids, care must be taken not to cut through high- or medium-voltage cables. These wires are not located in areas typically considered cut points. Do not cut the area inside of the passenger side frame rail since this is the location of high-voltage wiring in this particular model (photo 9).
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The response procedures for the GMC Yukon and Chevy Tahoe are similar to those of the other hybrid models on the road today. Be sure to take a moment to look for the presence of a hybrid vehicle and to employ all recommended safety procedures.
If you have been involved with an incident involving hybrid or alternative-fuel vehicles, please contact me at Jason@etsrescue.com. Case studies involving specific incidents will help further educate firefighters on the proper methodology for dealing with hybrids and other alternative fueled vehicles.
Jason Emery has been with the Waterbury (CT) Fire Department for 14 years and is assigned to city’s Rescue/Hazmat Company. He is an 18-year veteran of the fire service, a certified fire instructor, and holds a bachelors degree in fire science from the University of New Haven. He has taught extensively on the subject of hybrid vehicles and is an FDIC lecturer. He is the founder of Emergency Training Solutions, LLC and is the lead PowerPoint designer for the upcoming Fire Engineering Handbook for Firefighter I & II curriculum. He can be reached at .
