High voltage vs. low voltage.
All of the vehicles in the Hybrid Response Guide (HRG) are high voltage hybrids using 144 to 300 Volt traction batteries. These voltages can run up to 700 Volts at the inverter with the vehicle running. Obviously this amount of power can be lethal if not handled properly.
In contrast, the GM low voltage hybrids use 42 Volts. Other than a big spark or arc potential; these vehicles do not pose the same threat as their high voltage counterparts. The following paragraphs address the low voltage hybrids.
In 2004, General Motors introduced a line of so-called “Hybrid” trucks (Chevrolet Silverado and GMC Sierra) that utilize 42 Volts of power. The batteries used are three 12 Volt batteries connected in a series. These batteries differ slightly from standard lead cell batteries and have a minimal amount of electrolyte in them and therefore less spill potential. The trucks use the 42 Volt systems to automatically shut off the engine when coasting below 15 mph, during braking and when at a stop. The same system is used to start the engine and serves as a generator. To identify these “hybrid” vehicles, a blue Hybrid badge is located on the front doors. Also, the 120 Volt plug located in the bed, the APO switch on the dash and orange wiring under the hood and along the passenger frame are other clues as to whether the truck is a “hybrid”.
The GM “hybrid” trucks have a 120 Volt A/C power outlet located on the passenger side of the trucks bed and near the floor, under the center of the rear passenger seat. This system inverts the 42 Volts from the batteries to 120 Volts A/C. The system can easily be disabled with pushing the Auxiliary Power Outlet (APO) button on the instrument cluster (located to the right of the heater controls), shutting off the ignition switch and removing the key. In the event of a passenger side impact or front impact collision, sufficient enough to deploy the SRS, the 120 Volt systems will be shut down. Do not cut the orange wires that run from the generator on the passenger firewall to the bed of the truck on the passenger side.
Powering these vehicles down differs from High Voltage Hybrids in that they take 10 seconds to lose residual power as opposed to 5-10 minutes in high voltage hybrid vehicles. The voltage contained in these low voltage systems present an arc hazard but not a lethal amount of voltage.
Powering down the GM trucks consists of:
· Shutting engine off and removing the key.
· Disconnect negative battery cable located under the hood.
· Turn the 42 Volt Battery pack plug (green in color, located under the rear passenger seat on passenger side) from vertical to horizontal position. This will insure complete SRS power down and 42 Volt battery pack isolation.
· Wait 10 seconds for residual power to dissipate.
In 2007-08 Saturn and Chevrolet introduced their versions of low voltage “hybrids” with the Vue and the Aura as well as the Chevy Malibu. The Malibu and Aura are essentially the same, with some minor cosmetic changes. These vehicles utilize three 12 Volt batteries connected in a series to make 36 Volts DC. The batteries are Nickel Metal Hydride and use very little electrolyte so spillage is minimal in the event of battery case rupture. They use a blue coated wiring harness to ID the low voltage system.
Hybrid badges are used to help ID these vehicles, located on the front doors as well as the trunk deck. The engine covers have hybrid logos on them; a charge/assist gauge located on instrument cluster and auto stop at the tachometer is another way to tell it’s a hybrid.
There are many similarities between GM’s Low Voltage trucks and Saturn’s systems. Both use the 36-42 Volt system to start and stop the engine. The low voltage batteries cannot be used to move the vehicle. Fuel mileage is obtained through shutting off the engine upon deceleration or coming to a stop.
The voltage contained in these low voltage systems presents an arc hazard but not a lethal amount of voltage. Ten seconds is what is required to power down both the SRS system and the 36 Volt systems. By disconnecting the 12 Volt battery, it effectively powers down the 36 Volt systems, however a 10mm nut can be removed from the spring loaded cover which mechanically disconnects the 36 Volt system. In the event of SRS deployment, the 36 Volt battery pack will be isolated, as a contact inside the battery will open and discontinue power flow.
There are some differences in individual power down procedures per vehicle.
The 07’ Saturn Aura and the 08’ Chevrolet Malibu hybrids are as follows:
· Shut off the ignition and remove the key.
· If key is not accessible, remove the run/crank relay located in under hood fuse box.
· Disconnect both negative battery cables.
· Verify tachometer needle is pointing to off.
· Wait 10 seconds for power to dissipate.
The 2007 Saturn Vue hybrid is as follows:
· Shut off the ignition and remove the key.
· If key is not accessible, remove the 30 amp green Maxi fuse located in the under hood fuse block.
· Disconnect both 12 volt negative battery cables.
· Verify the tachometer needle is pointing to off.
· Wait 10 seconds for power to dissipate.
The 2008 Saturn Vue hybrid is as follows:
· Shut off the ignition and remove the key.
· Disconnect both 12 volt negative battery cables.
· If key is not accessible, cut the red cable attached to under hood fuse box.
· Verify the tachometer needle is pointing to off.
· Wait 10 seconds for power to dissipate.
