How To: 2004 Prius Navigation System Speed Sensor Defeat Switch

Author: Evan Fusco, MD - efusco on PriusChat
Originally posted on PriusChat here

*Disclaimer:  The modification below is taken at your own risk.  It could result in damage to your vehicle.  You could be injured or killed doing the modification.   It could void your warranty.  It could result in injuries if the Navigation system is used other than in the way it was designed.  Neither the author, Evan Fusco, MD nor nor anyone affiliated will be held responsible for injuries or damage resulting from any of the modifications.  If you choose to make these alterations to your vehicle you do so under your own risk and responsibility.  The information here is provided for informational purposes only and it is not suggested or advised that you carry them out.

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These instructions are for the installation of a switch in the 2004 model Toyota Prius which is equipped with the factory installed DVD Navigation system. The switch allows the occupants of the vehicle to temporarily disable the speed sensing system.

The speed sensing system has two functions:

  1. It enables the 'dead-reckoning' system which allows the vehicle icon to move smoothly on the MAP screen and may also assist the system in making the driver aware of turn and navigation instructions in the most efficient manner.
  2. It tells the Navigation computer when the car is in motion and disables direct address entry and other navigation search features as a safety tool to prevent the driver from attempting to use these distracting functions while the vehicle is in motion.

The author feels that there are many times when it is desirable to have the Navigation system fully enabled while the vehicle is in motion, in particular when there is a front seat passenger who is able to make those entries in the computer while the driver's full attention is on the road and driving.  By using this speed sensor defeat switch the passenger can temporarily disable the dead reckoning (which is unnecessary when entering navigation information anyway).  Once the information has been entered successfully, the switch is returned to the normal position and the system will work normally.  30-60 seconds after deactivating the speed sensor, the navigation system will detect, via the GPS feedback, that the vehicle is in motion. This will generate an error code and then disable access to the navigation buttons again. It is necessary to flip the switch momentarily then flip it back to regain access to complete your entries.

This modification does not disable the speed sensing for the Bluetooth® Phone system - that issue is still being investigated.

Required Items:

Time and Difficulty:

Process in Brief:

  1. Look under driver's seat for purple wire in the rightmost connector. Note size and color of violet wire so you can identify it elsewhere.
  2. Remove Arm Rest.
  3. Re-identify violet wire where it runs just under the edge of the carpet under the arm rest. Unwrap as much black tape as possible to expose wire and cut at midpoint and solder a 1 foot long extension to each end.
  4. Thread wires to switch site and replace armrest.
  5. Drill hole in armrest where switch is desired but won't interfere with cup holders, etc.
  6. Cut wires to appropriate length and install and solder wires to switch.
  7. Test

Detailed Process:
    **Before proceeding, be sure all power is OFF to your Prius.
  • Move the driver's seat as far back as it will go and poke your head under the front of it.  You'll see a number of white connectors with colorful wires poking out.
  • Identify the violet wire coming out of the top center of the plug on your right.  You'll be looking for that exact color and gauge of wire in just a minute.  You don't need to do anything else here.
  • Next you'll remove the center console/armrest.  This needn't be completely removed (there are wires connected underneath that make that more difficult and it's unnecessary), but you'll have to get it up out of the way to proceed.
  • You will now pull off the front cup holder assembly.  It comes out quite easily, if you find yourself forcing anything you're probably doing something wrong.
  • Get your fingers under the edge of the gray facing close to the bottom and pull outward and a little upward.  The entire piece should easily pull away from its clips.  Set aside.
    There are 2 screws at the front and 2 bolts at the rear that need to be removed.

    You'll need to remove any contents from the arm rest and the little felt pad at the bottom of the inside of the armrest console.  Use the 10mm socket wrench to remove those two bolts.


    Also use a Phillips head screw driver to remove the 2 front lower screws on either side of the console.  Now gently lift the console out of the way toward the back being careful not to pull any of the attached wires on the bottom of the console.


    There is a cut-out area of the carpeting.  Just under the edge of the carpet closest to the driver's floorboard you'll find a bundle or two of wires wrapped with black tape. (see wires-exposed ) Within one of those bundles you'll be able to see a hint of the purple wire from the first step.


    Strip away as much of the black tape as you can carefully do.  You should be able to get access to about 2-3" of exposed wire.  Separate out the violet wire.


    Cut the violet wire in the middle.  Now use the soldering iron and solder a 1 foot long length of your wire to the end of each now exposed end. (Hint: if you've not soldered before practice a bit to get comfortable; also, be careful with the hot iron so you don't burn yourself or your car or melt some important wire)  Wrap wires with electrical tape where you just soldered (or use heatshrink tubing).


    Tuck the main bundle back under the carpet.  Keep your newly attached ends out.

    Move the console back into place and thread the new wires up the inside of the console to the general location you will be putting your switch. Then fasten the console into place (or you can do it later after you've finished putting in the switch).


    Loosely replace the cup holder assembly so that you can see where a good site to place your switch will be such that it will be convenient to reach and yet not interfere with the function of the cup holders.  Mark that area with a marker.  Set the cup holder assembly aside again.  Drill your 3/4" (or appropriate size for your brand of switch) hole at the marked site.

    See diagram for installation site suggestion.  Some people prefer the switch on the passenger side since it should be a passenger programming the navigation instructions. Note: Some have also considered a timer switch that automatically closes the circuit every 40 seconds or so then automatically reopens it to allow you to continue to work.


    Secure the switch into place.


    Cut off the excess length of your wires and solder one wire to each connection point on the switch.

    Firmly reattach the cup holder assembly (not shown).

Start up your Prius and take it for a short drive.  While on the Destination screen you should see either all the buttons lit up and available to use or only the emergency button.  By flipping the switch the screen will go to the opposite.  I leave mine in the standard position so that map screen will function normally.  I'll flip the switch only to allow my passenger to enter destination information.  If you now switch to MAP screen with the switch in the 'normal' position you'll see the car icon moving smoothly across the road.  Now flip the switch…the icon will freeze in place for 20-45 seconds while the NAV system resets and the GPS signal is reacquired.  The 'dead-reckoning' has been disabled b/c the Navigation computer no longer knows how fast you're going.  Once the initial 'freeze' is done the car icon will move along the road properly but in a more 'jerky' manner and with less precision.  Once you've entered your destination information there's no need to leave the switch in the 'off' position, you can flip it back and the system should function normally. Remember that if, while you're entering information, the buttons dim you must close the circuit (by flipping the switch) briefly then flip the circuit open again to complete your entry. You may need to repeat that every 30 seconds to 1 minute.

Evan Fusco, MD
efusco on PriusChat
February 3, 2004


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