Frequently Asked Questions

What do the arrows mean on the Energy Screen?

If you are sitting still, there is nothing happening.
On the other hand, if you are moving, this is a condition known as "Glide."  In this state, your Prius is free-rolling under the power of inertia only.  Notice that there is no gasoline being consumed nor is there any power coming from the battery.  This is the true meaning of "free movement."

  

This condition normally occurs when you are sitting still and only when the battery is extremely low or the engine is cold.  Remember that the engine will operate if only to generate heat.  As long as it's warming itself, it might as well use the energy it creates to recharge the battery.

  

At times, the Internal Combustion Engine (ICE) will propel the wheels alone.  As you can imagine, this is one of the most fuel inefficient modes of operation for the Prius because all the power is coming from the consumption of gasoline.

  
           

This operating mode, called "Pulse" is when the ICE is powering the wheels but also generating enough energy to recharge the batteries.  This mode of operation can occur at speeds lower than 40 MPH but is also very normal at speeds above 40.  Since the ICE is required at speeds greater than 40 anyway, you might as well recharge the battery along the way.

  

At times, the ICE will not only power the wheels but will also send some energy to the electric motor to allow the motor to assist in the movement of the wheels.  This situation occurs occasionally during heavy load situations.

  

Also at heavy loads, you might see that the ICE is powering the wheels, diverting some energy to the electric motor, and recharging the battery all at the same time.

  
           

For real heavy load and/or heavy acceleration situations, both the ICE and the batteries provide power to the wheels and electric motor in order to move the car.  In this situation, both gasoline and electrical charge are being spent to propel the car.  Therefore, it's a good idea to limit the amount of time spent in this mode.

  

This mode of operation is called "Stealth" because the car is running entirely on battery and therefore is perfectly quiet.  The Toyota Hybrid Synergy Drive is currently the only hybrid model that allows a car to operate at speeds up to 42 MPH entirely in battery mode. 
Of course, this mode of operation depletes the battery and it must be recharged.

  

When you are not pressing on the accelerator, the rotation of the wheels turn the electric motor and generate electricity.  This electricity is routed to the battery for recharging.
The term "regenerative braking" is a misnomer because regeneration occurs also when you are rolling down a hill, for example.

  

 

How Come Some People Do Not Achieve the EPA Estimates Mileage?

The short answer is that the EPA tests are just plain bad.

The long answer is very well captured in a document written by Dr. Evan Fusco and can be found in our Resources section or just by clicking [HERE].

  

 

What is that Round Thing in the Front Bumper

The round plug on the driver's side of the front bumper is for towing the Prius.  Please note that this method of towing should be reserved as a last resort and you should never drag the Prius with the wheels locked.  The plug pops out to reveal a hole into which you can screw in the eye-bolt from the rear cargo area. 
1) Open the hatch and cargo area cover.
2) Remove the plastic cargo hold to reveal the spare tire.
3) Take the eye-bolt from its storage slot.  You'll know it when you see it; it's the thing that makes you say, "what's that for?"
4) At the front of the car, use a soft, thin tool (such as a credit card) to pop out the cover.  Don't use anything too stiff at the risk that you will scratch your bumper.
5) Insert the threads of the eye-bolt into the receiving hole and turn until tightly secure.  Righty Tighty; Lefty Loosey.

When finished, simply removed the eye-bolt, replaced the cover plug, and returned the bolt to the cargo area.

  

 

How Accurate is the MFD Miles per Gallon Calculations?

The calculation of the MPG is extremely accurate.  Here's why:
Very few people would argue that the Prius knows when the fuel injectors are squirting fuel into the engine.  Those same people would tell you that the amount of fuel injected is consistent.  So every time the Prius injects fuel into the engine, it simply keeps a running total of the amount of fuel consumed.  Of course, the Prius knows exactly how far it has traveled.  With these two amounts, it merely calculates the amount of gasoline used to travel the total distance.

But the MFD is not even close to my calculated mileage
Of course, there's a reason for that also.  The Prius fuel tank is more than simply a big empty drum like other vehicles.  To help control emissions, the Prius' fuel tank is lined with a fuel bladder.  This bladder is like a water balloon, expanding when you refill and shrinking as you empty it.

When the outside temperature is low, the bladder does not expand as much as it does in August when the bladder is warm and more flexible.  Therefore, you might be able to fit more gasoline in the tank in the summer than you can in the winter.  When you refill a fuel tank in a standard vehicle, the tank capacity never changes because it's a constant size and shape; this makes calculating the amount of fuel consumed very easy.  But in the Prius, where the bladder holds more or less fuel from refill to refill, consistent refill calculations are very difficult to achieve.

  

 

What the Heck is [B] Mode?

Myth 1) You must be in [B] mode for regenerative braking to work.  False.

Myth 2) Running your Prius in [B] mode will improve your mileage. Not necessarily.

If you have ever heard a semi truck's engine brakes - also known as "Jake Brake" - you understand that the engine can be used to slow the vehicle.  The reason is it is so loud in a truck is due to the size of the engine.  In the Prius, it works by shutting off the fuel injectors and using air compression to provide resistance to the pistons, thus slowing the engine and entire car. 

In Chicago, we don't really have overwhelming use for [B] mode.  However, in more mountainous terrain such as Appalachia and the Rocky Mountains, Prius drivers will shift into [B] mode to reduce their dependency on the brake pads.  This extends the pads' life considerably.

  

 

How Do I Work the Navigation System?

The Prius models equipped with the Navigation system came with a dedicated manual.  Please refer to that manual. 

If you want to know more or have specific questions, you will have an opportunity to discuss them at a meeting.