Service Guide, Unique Characteristics and Normal Operating Conditions for Two-Mode Hybrid

This bulletin is being revised to add the 2009 Cadillac Escalade Hybrid. Please discard Corporate Bulletin Number 07-00-89-059B (Section 00 -- General Information).

Notice: 

Caution: To reduce the risk of severe shock and burns, treat all high voltage cables and connectors as though they are energized until it can be verified that they are not.

Caution: Any service to the hybrid system or any related component requires the removal of the key from the ignition. If the key is left in the Run position, failure to remove the key from the ignition could cause the engine to auto-start, and in the Off position, the 300V system could remain active. The first step of disabling the high-voltage system is to remove the key from the ignition, which is designed to open the contactors in the battery pack, beginning the process of powering down the high-voltage system.

Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.

The High Voltage Disabling procedure will perform the following tasks:

Failure to follow the procedures exactly as written may result in serious injury or death.

Caution: The hood ajar switch communicates whether the hood is open or closed. If the ignition is in the "on" position and the vehicle is in auto-stop, the engine will re-start automatically when the hood is opened.

Drivers of the Two-mode Hybrid Tahoe or Yukon will experience some operating characteristics that are unique to these vehicles. Due to the quiet nature of the Hybrid Drive system, certain sounds that may have been masked by the engine's natural harmonics will be apparent. Among them is the electric engine cooling fan, the air conditioning compressor and the HVAC blower. In addition to those sounds, the drive motor battery assembly cooling fan, which sounds like the HVAC blower on low speed, may be heard from under the second row seat.

Key Crank Engine Start Sounds Different

This is a normal characteristic of the vehicle. If the engine will not crank, ensure that the 12v battery is sufficiently charged to allow for all of the hybrid control modules to "wake up" and initialize. The Two-Mode Hybrid does not use a conventional 12v starter- it uses one of the electric motors in the transmission to crank the engine that spins the engine faster than a 12v starter, resulting in different than typical starting noise.

Stall During Shift Out of Park Immediately following Engine Crank

This is a normal operating characteristic. Some drivers are able to interrupt the engine start sequence by immediately shifting the transmission out of Park after turning the ignition to Crank. Because the electric motor spins the engine so fast, the engine may appear to be running immediately after Crank but the ECM has not yet started spark and fuel. The ECM will turn off fuel and spark to the engine if it not running and the transmission has been shifted out of Park or Neutral. Inform the customer to wait 1-2 seconds before shifting out of Park or Neutral to ensure that the engine is running and has completed the start sequence.

Engine Restarts in Reverse/Manual Mode from Auto Stop

This is a normal operating characteristic - engine will restart any time the gear selector is in reverse or Manual Mode. Reverse remains in electric mode, however, the engine restarts to provide counter-torque for the internal transmission gears.

Slight Bump in Driveline during Acceleration

This is due to transition from V4 to V8 and vice versa. In Mode 2, the engine is able to operate longer in 4-cylinder mode under light throttle for improved highway fuel economy. As more power is needed, the system will transition in V8 Mode. This is a normal operating characteristic of hybrid powertrain to maximize fuel economy.

Low Pitch Noise during Auto Stop

This is a normal characteristic operation of electric coolant pump or hybrid battery fan. During Auto Stop the engine is not running and the interior cabin is quiet. These pumps run to keep the electronics from overheating, even in cold ambient temperatures. This noise may be more evident during high ambient interior temperatures. Advise the customer to keep the battery vents clear and not to carry cargo in the second row footwell area. The electric coolant pump runs in Autostop to circulate coolant to the HVAC system to maintain cabin temperature. That pump (under the right conditions) will run and may be barely audible.

Tailgate Hard to Close

To improve fuel economy, the tailgate of the Two-Mode Hybrid is made of aluminum, requiring more force to close and fully latch the tailgate.

Cruise Control Resume Operation

The Hybrid System is optimized for highest possible fuel economy. The Two-Mode hybrid vehicle resumes previously set vehicle speed at a rate which provides maximum fuel economy.

Brake Pedal Feel and Brake Pedal Vibration

12 Volt Operation

Grind/Growl in 4WD

On 4WD applications, the vehicle may experience a growl or gravel noise from the driveline momentarily during low speed, low RPM maneuvers. This is considered normal gear noise in the transmission.

Whine Sound during Electric Hybrid Operation

In electric drive mode and reverse, the transmission can be heard as the vehicle moves. This is a normal operating characteristic.

No Brake Assist (Hard Pedal) After Disconnecting Battery

Customers or technicians that are disconnecting the battery must wait for a period of at least 5 minutes with the ignition in the "OFF" position without pausing at ACCESSORY, and without applying the brake pedal prior to disconnecting the 12 Volt battery. These steps are necessary to allow the brake system pressure relief procedure to occur. Failure to follow these steps may result in warning lamps and/or DTCs being set pertaining to interruption of the pressure relief procedure. Other vehicle systems may also be affected by not allowing a 5 minute duration for power-down.

Engine

The Two-mode Hybrid Tahoe and Yukon feature an all-new aluminum block 6.0 Liter engine (RPO LFA, VIN code 5). This engine offers Late Intake Valve Closing technology. Closing intake valves after the intake stroke has completed allows reverse flow of the air/fuel charge into the intake manifold. This reduces the effective compression ratio, allowing the expansion ratio to increase while retaining normal combustion pressures. Efficiency is gained because the high expansion ratio delivers a longer power stroke and reduces the heat wasted in the exhaust. The lower effective compression ratio does mean less power, but it has been compensated for by increasing the mechanical compression ratio from 9.6:1 to 10.8:1, and the use of electric motors in the hybrid transmission. This engine also features Active Fuel Management, Variable Valve Timing, and an Electronic Throttle Control system. The engine does not have all the typical accessories on it. There is no generator, starter motor, belt-driven air conditioning compressor or hydraulic power steering pump on it. The LFA engine is not flex-fuel compatible.

The Gen-IV Vortec 6.0L hybrid engine features GM’s Active Fuel Management technology (AFM). AFM temporarily de-actives four of the eight cylinders under light load conditions. Working in conjunction with the hybrid control system, it provides significant fuel economy increases under the federal government’s required testing procedure, and potentially more in certain real-world driving conditions. Truck owners don’t have to compromise on the Vortec 6.0L's outstanding peak horsepower to go farther on a tank of gas.

The Vortec 6.0L for the hybrid application utilizes a variable displacement oil pump to minimize parasitic loss and thus increases fuel efficiency even further. Other Vortec Small Block engines use a fixed displacement gerotor pump, which can use up to 2 horsepower more to operate than the variable displacement pump. A series of vanes rotating in a carrier develops oil flow and pressure based on requirements from the engine. An internal spring/slider mechanism allows the pressure and flow to change in response to what the engine needs to operate everything in the lubrication circuit, from bearings to AFM to VVT.

The Gen IV Vortec 6.0L’s industry exclusive cam-in-block variable valve timing (VVT) is included in these hybrid applications, and allows the powertrain system to take advantage of late intake valve closing for greater efficiency. VVT eliminates the compromise inherent in conventional fixed valve timing and allows a previously unattainable mix of low-rpm torque, even torque delivery over a broad range of engines speeds, and free-breathing high-rev horsepower.

Two-Mode Hybrid vehicles utilize a specific aerodynamics package, a hybrid electric transmission, a higher efficiency engine and electrically powered accessories to achieve a fuel economy improvement of 30% combined and 50% city over the base models. Combined engine and transmission output is 369 bhp and 380 lb ft of torque, with 332 hp/367 lb ft coming from the 6.0L V8 Gen IV gasoline engine. The Two-mode Hybrid transmission adds the equivalent of the balance of the output, and in addition it increases the time the engine can remain at peak power during acceleration. The fixed gear ratios are designed to let the most power be used over the most useful vehicle speeds.

The Two-mode Hybrid vehicle is capable of operating in either full electric mode for under 45 km/h (28 mph) light acceleration, or in a blended gasoline/electric mode for higher speed or higher load request situations. These vehicles will not maintain auto-stop above 45 km/h (28 mph). How far or how long the vehicle will remain in auto-stop and operate in full electric mode is dependent upon drive motor battery assembly state of charge, electrical load (A/C, 12V accessory, and EPS operation) and temperature.

Transmission

The heart of the Hybrid system is the Transmission. (RPO M99, Hydramatic designation 2ML70) The Two-mode Hybrid Transmission contains two 60kW electric motors, each capable of producing 272 lb-ft of torque, 3 planetary gear sets, and 4 wet-plate clutches. The hybrid transmission can operate in multiple modes including propelling the vehicle electrically with the combustion engine off (auto-stop). Two continuous ratio modes of operation are attained with the electric motors, one with the combustion engine supplying torque, and the other with an electric motor supplying torque. Since the continuous ratio ability is attained with one of the electric motors, these modes are described as Electrically Variable Transmission modes or "EVT" modes. Three 300 volt A/C cables are connected to each of the two motors, these cables attach to the transmission housing via a rigid conduit around the transmission and are connected to an inverter that drives the motors. For maximum fuel economy, the transmission selector should be placed in Drive not manual mode. Four fixed ratios of 3.7:1, 1.7:1, 1.0:1 and 0.7:1 may be chosen in manual mode. The fixed ratios also let the transmission save battery power that would otherwise be used to control range of the variable ratios to keep the engine in its optimal rev range. Fixed ratios also allow overdrive, for faster overall total speed of the vehicle. Fixed gear changes are accomplished with clutch-to-clutch control, where an oncoming clutch is engaged and an "offgoing" clutch is released in a precise manner to achieve the ratio change. The first-to-second upshift, however, is a freewheeling action, where the second gear clutch engages while the first gear one-way clutch spins freely. This allows a greater degree of smoothness at lower vehicle speeds. The Electric motor/generators in the transmission can be used either to propel the vehicle or to generate power to charge the drive motor battery assembly. The transmission control module (TCM) is located inside the transmission.

All vehicle movement in reverse is performed by the electric motors in the transmission. In order to maintain the proper charge in the drive motor battery assembly, the engine will run when the vehicle is in reverse, however, there is no mechanical connection between the engine and the drive wheels in this range.

This transmission has no torque converter. There is a fluid-filled torsional dampener located between the flexplate and the input to the mechanical transmission fluid pump. This transmission has an auxiliary transmission fluid pump, which is located external and below the bellhousing. It is controlled by the auxiliary pump controller, which is mounted below the 12V battery on the left side of the engine compartment. The aux pump operates during auto-stop and provides transmission fluid to the electric motors for cooling and to maintain clutch pressure. Due to the heat generated by the 60Kw electric motor/generators, there is an auxiliary transmission cooler that is specific to this application.

DEXRON®- VI is used as a lubricant and to cool the electric motors. For normal use, there is no fluid change scheduled. DEXRON®-VI was developed to have a more consistent viscosity profile; a more consistent shift performance in extreme conditions; and less degradation over time.

The Two-mode Hybrid Tahoe and Yukon are offered in both 2WD and 4WD configurations. The transfer cases in the 4WD models are identical to transfer cases found in the base model application. Recreational or Dinghy towing is only permissible on 4WD vehicles with the transfer case in neutral and the transmission output shaft held stationary in Park. Under no circumstances can a 2WD vehicle be dinghy towed or the transmission output shaft be allowed to turn.

Important: Wrecker towing is to be done by flatbed carrier only.

Drive Motor Battery Assembly

The drive motor battery assembly is serviced as a unit at this point.

The drive motor battery assembly is also known as a battery pack. The drive motor battery assembly is housed under the second row bench seat, and is enclosed in a steel box. Inside the drive motor battery assembly is a set of NiMH battery cells, the controller, a cooling fan, and a set of contactors that will engage only when the controller tells them to. When the controller indicates it is okay to close the contactors within the drive motor battery assembly, the series-wired NiMH battery cells and their 300V of potential are connected to the rest of the Hybrid system.

One input to the drive motor battery assembly controller is the High Voltage Interlock Circuit system, or HVIC system. The HVIC system is comprised of a series of switches that if opened, may command the controller to open the contactors of the drive motor battery assembly. This will prevent the Hybrid system from operating. These switches are located in the following locations:

PIM/APM (Power Inverter Module/Accessory Power Module)

The Power Inverter Module (PIM) and Accessory Power Module (APM) are located under the hood on the right side of the engine compartment and are referred to as the Drive Motor Control Module Assembly. The PIM is a high voltage high speed switching device that uses 300V DC and converts it to 300V 3 Phase AC to power the electric motors in the transmissions during Hybrid operation. The PIM is also able to take 300V 3 Phase AC from the electric motors, either during battery charging, or during a regenerative braking event and convert it into 300V DC to charge the drive motor battery assembly. The PIM can get very hot during operation, so a discreet cooling system has been integrated into the design. Included in the power electronics cooling are:

It is important to note that while the power electronics cooling system uses DEXCOOL, IT MUST be mixed with deionized water to prevent corrosion within the PIM/APM assembly. Pre-Mixed DEXCOOL contains the correct ratio of de-ionized water and should be used to service the power electronics cooling system. This coolant does not mix in any way with engine coolant.

The APM is a module that converts 300 Volts to provide a 12V power feed to keep the standard service battery charged. It also provides a 42V feed for the Electronic Power Steering.

Tire Inflator Module

The Two-mode Hybrid Tahoe and Yukon feature a tire inflation kit instead of a spare tire. In the event of a flat tire, the tire sealer should be used in combination with the air compressor to inflate the tire. The tire inflation kit is located in the left rear storage compartment, where the jack is normally located. It is important to note that there is no spare tire, and the tires are not run-flat tires. Any tire or wheel damage that is not repairable with the tire sealer and air compressor requires that the vehicle be flat-bed carried to the nearest tire repair facility.

Aerodynamic changes

The Two-mode Hybrid Tahoe and Yukon offer improved aerodynamics over the standard Tahoe and Yukon. The improvements are achieved by a multitude of changes. The following are some of the aerodynamic changes:

These changes have enabled about a 2% decrease in wind resistance, in addition to weight savings, which translates into better fuel economy.

Brakes

The service brakes on the Two-mode Hybrid Tahoe and Yukon are unique. The base brakes are blended with electric motor braking and a brake pedal emulator provides feedback to the driver. There is no vacuum brake booster for the master cylinder. Instead, there is a hydraulic accumulator and a high-speed, fast acting pump that provides brake pressure boost to the hydraulic system. ABS and Stabilitrak are a standard feature of the Two-mode Hybrids.

EPS (Electronic Power Steering)

Power Steering on the Two-mode Hybrid is achieved without the use of a hydraulic rack and pinion and belt driven pump. For these models, power steering is achieved with a rack-mounted 42V electric assist motor. Using an electric motor instead of a belt driven pump and hydraulic rack enables power steering operation to continue while the engine is in auto-stop.

Air Conditioning

The Two-mode Hybrid SUV's have no belt drive air conditioning (A/C) compressor. Instead, there is a 300V A/C compressor that bolts into the same location as a standard belt-driven A/C compressor. The A/C compressor includes a high-voltage A/C pump and an inverter module that converts 300V DC from the APM into 300V 3-phase alternating current. The A/C compressor is serviced as a unit, and uses POE (Polyol Ester) refrigerant oil instead of PAG (Polyalkylene Glycol) because it is less hygroscopic. The purpose of using an electric air conditioning compressor instead of a belt driven compressor is to provide air conditioning performance while the engine is in auto-stop. The A/C compressor features a high RPM scroll compressor that is pulse width modulated. During conditions with high ambient temperatures and high humidity, the driver may notice a unique high-pitched sound from the compressor. This is considered a normal characteristic, and it will be heard most noticeably in auto stop mode with the window lowered.

Weight Savings

With the deletion of the spare tire and roof rack, weight savings was achieved. Above and beyond that, engineers worked hard to find solutions that would offset the additional weight of the drive motor battery assembly and transmission assembly. They achieved that offset by utilizing premium materials that, while offering less mass, are just as strong as the materials traditionally used. Front lower control arms are made from aluminum, as is the front bumper bar, the hood, the rear decklid, and the rear propeller shaft. Special low-mass wheels have been designed and are used to reduce unsprung weight. Premium aluminum frames and thin, low-profile foam has been used in the front seats, and the second row seat was redesigned to incorporate the drive motor battery assembly, as well as to reduce weight.

Other Standard Features

Navigation radios are standard in the Hybrid Tahoe and Yukon. In addition to the functionality of the navigation system, there is an additional feature that is unique to the Hybrids. When utilizing the navigation system users will notice that under the MENU tab, there is a graphic display of the hybrid system and its operational state. When the vehicle is in auto-stop, the display indicates that the engine is not running and the vehicle is not moving. When the vehicle is in mode one, the display indicates that power stored in the drive motor battery assembly is being used to propel the vehicle forward. When the vehicle transitions to mode 2, the display indicates that the engine is propelling the vehicle, and the electric motors are helping (Hybrid mode). When the vehicle is braking, it indicates that there is electricity being generated and stored in the drive motor battery assembly for future use (Regen mode). A 110V, 150W power outlet is located behind the third row of seats along the window sill near the tire inflation kit. Typically, 150 watts is enough power to charge two cell phones, charge one laptop, or maintain two laptop charges, but is not intended for heavy-duty usage.

Below are accessories that have been approved by Service Parts Operations (SPO) at this time:

Below are other accessories that SPO is exploring for possible future release.

Important: The following are some items that are not approved to be used with this vehicle:

Essential tool shipments for select dealers (Visual Display Eligible) have been completed. Future Hybrid Essential Tool shipments will be based on training completion. Hybrid essential tools will be shipped automatically to dealers meeting Hybrid training requirements. If immediate assistance is needed for Hybrid tools, contact SPX at 1-800-GMTOOLS (prompt #4 then prompt #1) and request GM Two-Mode Essential Tools. Provide the customer service agent with dealership information as requested. Tools will be invoiced through dealer parts account.

Safety Gloves & Sleeves

Three sets of rubber electrical insulation gloves (S, M, L) and protective leather sleeves will be direct shipped from the glove manufacturer. They should be stored in EL-48900 Safety Kit.

*Visit the North American Independent Laboratory website at www.nail4pet.org for an accredited laboratory for re-certification.

For future classes, visit GMTraining.com.

Dealers in Canada should refer to the latest training availability in the GM Canada Product Service Training Course Catalogue located on GM infoNET under Service & Body Training.

The Two-mode Hybrid Tahoe and Yukon vehicles will have multiple warranties on them. The hybrid powertrain will carry an 8 year, 100,000 mile (160,000 kilometer) warranty. The non-hybrid specific powertrain will carry the same 5 year 100,000 mile (160,000 kilometer) coverage as the base truck. The emissions warranty and bumper-to-bumper (Base Warranty in Canada) has not changed.