Toyota Prius Service Precautions

Introduction

The 2001 Toyota Prius is a hybrid vehicle (HV), featuring the Toyota Hybrid System (THS), a new type of power train combining gasoline and electric drive sources. It is equipped with a 1.5 liter 4-cylinder gasoline engine and an electric motor that deliver power to drive the vehicle. Depending on driving conditions, one or both of the power sources may be used to maximize fuel efficiency and minimize emissions.

The Prius differs from conventional vehicles by nature of its unique electrical system, which includes a nickel-metal hydride (Ni-MH) battery pack and high-voltage circuitry capable of producing nearly 300 volts. The high voltage components require special handling procedures that must be followed whenever the vehicle is inspected or serviced. This can include, but is not limited to routine maintenance, collision repair, vehicle recovery and occupant rescue.

Careless or improper handling of the hybrid system can result in severe injury or electrocution. Furthermore, Toyota cautions that only a Toyota Hybrid System qualified technician can perform THS service.

High Voltage Components

HV Battery

Wiring Harness

Service Plug

The service plug must be removed before dismantling any part of the high voltage system. Removal of the service plug cuts power to the car's high-voltage circuit, but it does not disable the individual batteries.

Transaxle

The transaxle contains two electric "motor generators" (one for driving the vehicle and one for generating electrical power), a power splitting device and a gear reduction unit.

Inverter

The inverter is an electric power controller that converts and regulates the electric current between the motor generators and the HV battery. It converts high-voltage DC (direct current) from the HV battery into three-phase AC (alternating current), as well as converting the AC current from the motor generators into DC.

DC-DC Converter

The converter transforms high-voltage DC (273.6 volts) to low-voltage DC (12 volts) to supply electricity to various body electrical components such as the headlights, audio system and cooling fans. The converter is also used to recharge the 12 V auxiliary battery.

Precautions for Inspecting or Servicing the Engine Compartment

The vehicle can still be driven (propelled by the electric motor generator) in this mode (READY lamp ON) even if the gasoline engine is not running.

Always remove the ignition key before inspecting or servicing the engine compartment.

Precautions for Servicing a Damaged Vehicle

1. Wear insulated or rubber gloves, goggles and safety shoes.

2. Do not touch a bare cable that could be a high-voltage cable.

   If it is necessary to touch a high-voltage cable, or there is a possibility of making accidental contact, be sure to:

   • Wear insulated gloves

   • Measure the voltage between the body and ground using an electrical tester (volt meter).

   • Insulate bare cable using vinyl electrical tape

3. Check the HV battery and the nearby area for possible leakage.

   If any liquid is noticed, assume that it is battery electrolyte (battery "acid"). The electrolyte from the HV battery contains potassium hydroxide, a highly alkaline solution that can react with zinc, aluminum and other metals to produce flammable hydrogen gas. Potassium hydroxide in also extremely hazardous to body tissue. Proper procedures must be followed to neutralize the electrolyte:

   • Wear rubber gloves and safety goggles or a facemask. Clothing items made of leather or wool will not protection you from the electrolyte.

   • Apply a red litmus paper to the leak. If the paper turns blue, neutralize the liquid with a saturated boric acid solution. (made by mixing boric acid powder in water until the powder will no longer dissolve. Boric acid is available at most pharmacies.) Reapply a red litmus paper to make sure it does not turn blue.

   • Wipe off the neutralized liquid using waste rags.

   CAUTION!

   If electrolyte adheres to any exposed skin, wash the skin immediately using the boric acid solution and large amounts of water. If the electrolyte adheres to any article of clothing, take it off immediately. If the electrolyte comes in contact with your eyes, do not rub, but rather rinse them with the boric acid solution or large amounts of water. Seek immediate medical attention.

4. If the HV battery is damaged, contact a Toyota Dealer or Toyota national distributor for battery disposal information.

5. If damage to any of the high-voltage components or cables is suspected, disconnect the high-voltage circuit by using the following procedure:
   
   • Move the shift lever into "PARK" and engage the parking brake.

   • Remove the ignition key. Then, disconnect the cable from the negative terminal on the auxiliary battery.
     

   • Wearing insulated gloves, remove the service plug.
     

   • If the service plug cannot be removed due to damage in the rear portion of the vehicle, remove the HV fuse or IGCT relay.
     
     

Precautions for Inspecting or Servicing the High-Voltage Circuit

1. Be careful not to touch any of the high-voltage wiring (colored orange) or components (marked with High-Voltage caution labels).

2. Wear insulated gloves.

3. Remove the service plug from the vehicle to prevent possible electrocution. Keep the service plug in a safe place (like your shirt or pants pocket) to prevent anyone else from reinstalling it while you are servicing or inspecting the vehicle.

4. Wait five minutes after removing the service plug before touching any of the high-voltage connectors or terminals. It takes five minutes for the high-voltage condensers inside the inverter to discharge.

5. Before touching a bare high-voltage terminal, use an electrical tester (volt meter) to ensure that terminal is not charged with electricity.

6. Use vinyl electrical tape to insulate any disconnected or exposed high-voltage terminal or connector.

7. The screw of a high-voltage terminal should be tightened to the specified torque. Insufficient or excessive tightening of the screw can cause failure.

8. After servicing the high-voltage system and before reinstalling the service plug, check that:
   
   
   • All tools, parts or metal objects have been removed from the vehicle.

   • The high-voltage terminal screws are firmly tightened to the specified torque.

   • All connectors are fully engaged.

9. Reinstall the service plug and reconnect the cable to the negative terminal of the auxiliary battery.

Auxiliary Battery

The following conditions may indicate that the 12 volt auxiliary battery is depleted:

• No display appears on the instrument panel when the ignition switch is in the ON position.

• The hybrid system will not start.

• The headlights are dim or dark

• The sound from the horn is weak.

Never use a quick charger to re-charge the auxiliary battery.

The proper re-charge procedure is as follows:

1. Move the shift lever into the "P" position and engage the parking brake.

2. Remove the key from the ignition switch.

3. Remove the luggage compartment lower side cover.

4. Connect the 12 volt battery of the rescue vehicle to the Prius auxiliary battery as shown.
   

5. Start the engine on the rescue vehicle and run the engine at a speed slightly higher than idle to charge the Prius auxiliary battery.

6. Turn the ignition switch to the START position to start the hybrid system.

7. Remove booster cables in the opposite order of the connection procedure.

If the auxiliary battery needs to be replaced, replace it only with a 12 volt battery specifically designed for use in the Prius.

Towing Precautions

1. Disconnect the cable from the negative terminal of the auxiliary battery and remove the service plug before towing the vehicle.

2. Always tow the damaged vehicle with the front wheels or both front and rear wheels off the ground. Towing the damaged vehicle with its front wheels on the ground may cause the motor to generate electricity. Depending on the nature of the damage, electricity could leak and cause a fire.

The information provided in this bulletin is for educational purposes only. Although every effort has been made to ensure the accuracy of the information contained in this bulletin, Tech-Cor assumes no responsibility or liability for any repairs performed using information from any publication issued by Tech-Cor.

Any person performing repairs must determine whether any suggested or recommended procedures or repairs are suitable or appropriate for the particular vehicle being repaired. The repairer remains solely responsible for such determination, as well as for the proper completion of the repairs.

Reproduction of this bulletin is not permitted without the written approval of Tech-Cor.