Remote Starter by Viper model 5900 for 2007 Prius

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How would this work with SKS? The remote start we had installed in my daughters car required us to bury a key under the dash so it would recognize that there was a key nearby in order to remote start the car.

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I've been pondering how to connect a remote start to my Prius for some time. The problem is that all of the units I've looked at are designed for conventional cars.
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The sequence of events on with a conventional remote start is:

1. Start request initiated from remote.
2. Pulse security disarm.
3. Enable key bypass
4. Enable ignition
5. Enable starter
6. When tachometer signal indicates engine running, disable starter.
7. If engine doesn't start within several seconds, disable starter, disable ignition, wait a few seconds, and retry the start (up to 3 times).

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The sequence of events required for a remote start on the Prius is:

1. Start request initiated from remote.
2. Pulse security disarm (I'm guessing here - I haven't tried it yet).
3. Apply brake signal (required to get to Ready mode)
4. Delay a short time (1/10 second?)
5. Pulse Power button pressed signal (2 circuits, although either one works alone).
6. Watch 12 volt power jumping to about 13.5 volts. Most remote start devices have a "voltage sense" method of detecting engine start, and this should work with the Prius. The inverter that charges the 12 volt battery kicks in with Ready mode, providing the same voltage change as an alternator does with a conventional car. If the remote start device does not have "voltage sense", then you have to provide a tachometer type signal that indicates a successful start. If you don't indicate a successful start to the remote start device, then it will disable the ignition and retry the start process.

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In order to stop a conventional car, the ignition circuit is disconnected.

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In order to stop the Prius, the Power button is momentarily pressed.

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There is obviously a mismatch between the control signals that a conventional remote start device provides, and the control signals that the Prius requires. I've designed a control board that uses 6 relays to handle the conversion. It's untested, so I'll just provide the logic that I think will work. Note particularly that the remote start device ignition signal is treated as logic only - it is NOT connected to the car ignition circuit.

Case 1: Remote start raises Start signal
<blockquote>Enable key bypass
Delay 1/10 second
Enable Power button signal</blockquote>
Case 2: Remote start raises ignition signal
<blockquote>If the car ignition is already on, cancel the remote start</blockquote>
Case 3: Car ignition turns on
<blockquote>Disable Power button signal
Disable key bypass
Hold "car ignition on" status</blockquote>
Case 4: Remote start ignition signal drops
<blockquote>Enable Power button signal for 1/10 second</blockquote>
Well, that's what I remember about the circuit just now. I'm still fiddling with it so reality will probably require some changes. It is extremely important that the remote start device cannot interfere with the car as it's traveling down the road. I don't want a stray radio signal, or even a press of the remote killing the ignition while the car is in motion.

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Now, about the key bypass. Most modern remote start installations use a transponder bypass device that substitutes for having a key in the ignition. This is either an actual key with some electronics to relay the transponder signals to the ignition switch, or an electronic box that acts like the transponder in a key. The Prius has a transponder in the keyfob that is sensed when you put it in the keyslot. I attempted to install a KEY-OVERRIDE-SL2 device which is supposed to mimic an actual key. Doesn't work. I got it programmed, but the Prius doesn't believe that it is a proper key. I next attempted to use a real keyfob (battery removed) in a universal bypass box. Didn't work, although in theory it should if there is adequate signal transfer to the keyslot.

The only way viable way I can see to satisfy the requirement for a key is to use a real keyfob. The keyfob battery must be replaced with power supplied from the remote start system. Power to the keyfob must be applied during the start sequence, and could be left on while the car is in use. The keyfob power must be disabled when the car is not running. Note the requirement of 3 volts for the keyfob. If you just switch the existing battery, then you're going to have to replace the battery every few years (just tear apart the dash...).

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$800 to install a remote start on the Prius is not out of line. There is a lot of conversion logic required to use existing remote start devices, plus you have to donate a real SKS keyfob. I checked several places about how much it would cost to have a unit installed. Every answer was a refusal to even bid.

 

It sounds like you're way ahead of me in getting a remote start. But your experience underscores the fact that the Prius is quite different from a conventional car. In addition to the logic that I described above, the remote start system should shut down when a door is opened, or at least when the brake is pressed. Another lockout technique would be to disable the gear selector when in remote start mode.

The keyfob needs to be disabled most of the time. It is only needed during the start sequence. The way to disable the keyfob is to remove the battery. Then apply 3 volts power to the battery connections during the start sequence, but not the rest of the time.

I don't understand why the car can be entered while the engine is running. When I leave the car on (for the air conditioning), the only way I can lock the door is with the mechanical key. When I return, the mechanical key is the only way to unlock the door. The keyfob system is disabled when the power is enabled with the Power button. Any variation from this behavior is due to the installer changing the system.

 

Not an expert, but who would want to vandalize locked but running Prius? Who would want to steal it for parts or joy ride? This is a little bit too much. I am working in parking lot and I be seen many many old cars having weird sophisticated alarm system installed (in contrast with original fob) I could not understand until recently, it’s all done for one things only, the ability to remote start your car. If you so concern about security of your car, let it run for 10 minutes without the fob, then it will shut down, then you can use timer on your phone for 9-10 minutes and relaunch your engine again. This is without the need for fob key in the car