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TOPIC: GMC and Chevrolet 2008 model year two-mode hybrid vehicles
OBJECTIVE: Understand the design and operation of a 2008 model year or newer GM two-mode hybrid vehicle such as a Tahoe or Suburban
TASK: The fire, EMS and/or rescue team shall inspect a 2008 model year GM two-mode hybrid vehicle and be able to identify the major hybrid system components, explain the normal operation of the hybrid system, and identify the recommended emergency procedures for dealing with this vehicle at a real-world incident.
The 2008 model year GMC Yukon and Chevrolet Tahoe two-mode hybrid vehicles are gasoline-electric hybrid SUVs that were introduced in the fall of 2007. Each vehicle is equipped with a special V8 gasoline engine that can operate as a fuel-saving four-cylinder engine under certain conditions. To gain improved miles-per-gallon ratings, especially under city-driving conditions, the Tahoe and Yukon hybrids use a 300-volt electrical system coupled with a unique hybrid transmission. There are two very compact electric drive motors packaged within the transmission housing that can move the vehicle totally on electric power, called the electric mode, at up to 25 miles per hour. The SUVs also have a 42-volt and a traditional 12-volt electrical system.
The "two-mode" term comes from the two different combinations of power that can move the vehicle. For the Chevy Tahoe and GM Yukon, during low-speed, light-duty driving, the system works like a conventional single-mode hybrid electric vehicle, shutting off the V8 engine whenever possible, allowing one or both of the electric motors to move the vehicle.
During highway cruising, the two-mode system can also use one or both electric motors, but this time they function to provide a power boost to the vehicle along with the power from the gasoline engine. In addition, the V8 engine uses technology systems such as variable valve timing and cylinder shutdown to save fuel. For the driver of the SUV, the transition between the two modes is completely seamless.
GM engineers took great efforts to reduce the weight of numerous vehicle components, which keeps the Tahoe and Yukon Hybrid models in the same weight class as their gasoline-only twins. At a crash scene, therefore, responders will encounter an aluminum hood, aluminum liftgate with fixed glass and 18-inch cast aluminum wheels along with an aluminum front bumper beam.
The Option for Four Roof Airbags
Standard safety features that are important to responders include dual-stage frontal airbags, roof-mounted side-impact airbags that are rollover enabled and front seatbelt pretensioners. Worthy of note is the fact that there can be four roof airbags on these vehicles; two bags on each side. One roof airbag on each side is standard equipment. One stored-gas inflator is mounted horizontally along the roof rail to deploy the roof airbag that protects the front- and second-row occupants. If the optional third-row seating is ordered, a separate stored-gas inflator secured to the D-pillar will also be present. This roof airbag deploys to protect the third-row seat occupants. This is a total of four roof airbags and four high-pressure inflators. Strip the trim for sure!
Special emblems, called badging, are used to identify the 2008 GMC Yukon and Chevrolet Tahoe hybrid vehicles. There are emblems located on both front fenders, decals on both front doors, green "H" badging on both C-pillars, a green "H" on the lower right corner of the vehicle's liftgate, and hybrid decals on the rear window and the top of the front windshield. When the hood is opened, indications that a two-mode hybrid system is present include a hybrid label and a high voltage warning label on the power electronics cover.