I built one just for this tutorial. It's not quite done yet. It has a switch to turn it on and off so don't worry about it constantly being on. It's not good for the nav with the speed lock constantly bypassed. Bypass it only when you need it. Anyways keep voting to show your interest or the lack of. As you can see from my profile, I have a 2010 Gen III Prius V with ATP. It came with nav. I can't replace it b/c of the parking assist. ------------------------------------------------------------------------------------------------------------ Edit: Moving Original Post here ------------------------------------------------------------------------------------------------------------ Background ​ Navigation speed lock activates when the vehicle's speed exceeds 5mph. It locks out almost every function so you can't manipulate majority of the settings. I've been running the speed lock bypass that I built for almost a year with no problems so I thought I'd show you guys how to do it. This is a basic step by step on how to bypass the navigation speed lock on Gen III Prius with factory navigation system. I'll also try to explain the basic concepts of it. You do need some soldering skills. Warnings ​ 1 - Operating the unlocked navi is worse than texting while driving. It takes your eyes off the road. I will not responsible for your actions as a result of this modifications. 2 - I have broken down each step as easy as I can. If you get lost following my direction, don't blame me. If you build it and failed to function as described, don't blame me. 3 - Because this is a DIY project, there's no telling weather it'll work for your navigation system or not. I will not be responsible for any damages to your navigation system or your vehicle caused by this modification. Basic concept ​ The factory nav system has a speed sense wire coming from the vehicle. It uses this signal to determine vehicle speed and not the GPS signal. (If it was GPS based, this bypass would not be possible) It locks out a lot of functions when the speed exceeds 5mph. If you think you can use voice activation, you better know exactly how it works because if you ask for help on the voice commands, it will tell you to stop the vehicle. This pretty much defeats the purpose of voice control. [FONT="e]In order to bypass the speed lock, the nav system must receive a speed signal of less than 5 mph. The speed signal for most Toyotas is 4 pulse per tire rotation as shown in this picture. This includes the Gen III Prius.[/FONT]  Source Navigation Input Override (Speed Sensor Bypass) | PriusChat Thanks to rachaelseven for posting it. I believe Gen II also uses this signal. If it does, this will also work on Gen II. You just have to locate the speed sense wire behind the display. [FONT="e]Check out Prius Speed Wire for Gen II VSS wire location.[/FONT] In order to reactivate nav, phone, audio and settings control, we need to build a circuit that simulate a speed below the speed lock threshold and feed that signal to the radio regardless of what the vehicle speed is. We can do this by building an astable 555 timer circuit and time it at less than 4 cycles per second. [FONT="e]According to my calculations 215-45-17's RPM is 819 rev/mile 1mph = 819RPM/60minutes/60seconds= .2275hz. There are 4 pulse per tire rotation so .2275hz*4= 0.91hz per mph. [/FONT]According to brosnan at Navigation Input Override (Speed Sensor Bypass) | PriusChat speedSignalFrequency > 6.04Hz : begin lockout speedSignalFrequency < 4.80Hz: release lockout A lot of the information can be found in this thread Navigation Input Override (Speed Sensor Bypass) | PriusChat Shortcuts ​ There are none that I know of. Do not cut the speed signal wire and leave circuit open. I've spent a few days analyzing the speed signal trying to learn as much as I could. The speed signal alternates between positive and negative 14v at less than 1mph. As speed increases, the pulse increases and the voltage decreases because of the faster alternating frequency. Knowing that it alternates between positive and negative, I analyzed the signal when parked. Just as I suspected, the speed signal rests at either positive 14v or negative 14v at complete standstill. Don't get your hopes up thinking that you can just feed a positive or a ground into the speed signal wire. It will only work for about 70 seconds. I timed it. After that it goes to dead reckoning and locks you out because it uses GPS signal to determine vehicle speed. Reconnecting the speed signal continues the speed lock out for additional minute or so. The gyro sensor continues to work even at artificial 0mph. I don't know if it gets heading from the GPS signal or an actual compass. Parts You'll Need ​ The parts you need are 555 timer radio shack part# 276-1723 RadioShack LM555 Precision Timer (8-Pin DIP) - RadioShack.com 8 pin IC socket RSP# 276-1995 8-Pin Retention Contact - RadioShack.com (Optional for easy soldering) 4.7uf capacitor RSP# 272-1024 4.7 uF Electrolytic Capacitor - RadioShack.com .01uf poly-film capacitor RSP# 272-1065 0.01µF 50V 10% PC-Mount Capacitor - RadioShack.com 1K Ohm 1/4W resistor RSP# 271-1321 1K Ohm 1/4-Watt Carbon Film Resistor (5-Pack) : Resistors | RadioShack.com 1/4w is enough If it's not available, 1/2 is OK too. 1M Ohm 1/4W resistor RSP# 271-1356 1M Ohm 1/4-Watt Carbon Film Resistor (5-Pack) : Resistors | RadioShack.com 1/4w is enough If it's not available, 1/2 is OK too. Diode RSP# 276-1103 1N4004 Micro 1-Amp Rectifier Diode : Diodes | RadioShack.com 3/32" heat shrink 3/16" heat shrink electrical tape (3M Super 33+ works best) black zip ties 6' of 18awg red, black, blue, violet, orange wires. I chose these colors because they are readily available from any stereo shops. You can use whatever color you want. To keep it simple, you gotta have 5 different color wires. ON-OFF SPST rocker switch. 2 SPDT relay. 2x blue T-Taps 4x pink T-Tap terminals 15x pink or blue shielded 1/4" speaker terminals ​ Tools you'll need ​ crimper similar to Channellock 909 wire stripper similar to Channellock 957 heat gun solderingiron with fine tip and solder 12v battery LED lights for testing (see the signal visually) multimeter for testing oscilloscope for testing (optional) Before we begin, take a look at Astable 555 Square Wave Calculator for calculating the 555 timer. That site shows the most accurate depiction of an actual 555 timer and its terminals and where each terminal connects. According to the calculator, C = 4.7uf (0.0000047f), R1 = 1K ohms +-10%, R2 = 1M ohms will yield 50.025 duty cycle. R2 determines the slower frequency. It must be 39k or higher. Lower than 39k will result in faster frequency and the lockout won't get overridden. Also look at Convert microfarad to farad [SI standard] - Conversion of Measurement Units for converting microfarad to farad. The build ​ Instead of building a circuit on a breadboard or an actual circuit board, it'll be easier and faster to build it as a harness. The wires are basically traces on a PCB.