SKS always searching?

No, the search mode turns off once the car is in Ready mode. The search signal is at 134.2 KHz, and I've picked it up on a long wave radio receiver at double that (269 KHz on my radio). It sounds rather like a sonar bleep in WWII submarine movie. The bleeping is on outside the car when it's locked. The signal changes when a keyfob is recognized (about 3 feet from the door), and switches to inside the car once the car is unlocked. When the car reaches Ready mode, it turns off.

 

Interesting! Makes me want to break out the spectrum analyzer and push it over to the car!

 

Now what would be really interesting would be to decode the messages. The 134.2 KHz signal is quite short. Only registered keyfobs reply to it, so there must at least be a car id in the message. On receipt, a registered keyfob responds on 315 MHz with a quite long and varying message. It wouldn't surprise me if the car signal is the same message each time. The keyfob reply varies with each keypress/reply.

 

I am fairly certain it is a rolling code, so the car will send a code and the fob has to match it and send back a coded message that "matches". After so much of a timeout or so many presses I am sure the code changes to something else psuedo-randomly.

The problem is without knowing the decoding clock signal, it is very hard to decode it. Different clocks make different messages. The best guess would be to capture a bunch and use the smallest signal change captured to figure out the clock, but who knows.

315Mhz is the standard unlicensed band, and I have built a few projects using that frequency. I might have some hardware already on my shelf to output that frequnecy to a standard scope making it super easy lol.

 

While you're at it, the 134.2 KHz signal must vary in either message or timing between the various transmitters. So is the message the same from both front doors on a 3 door SKS? Do both doors transmit at the same instant, or are they staggered? The car knows where the keyfob is, so the transmitter (actually, they call it an oscillator) which triggers a keyfob reply must identify the keyfob location.

 

The 134.2 message is really short. I haven't decoded it, but would guess that it can't be longer than maybe 8 bytes. All keyfobs have to understand that message, so a rolling code doesn't make much sense for the polling. The keyfob message on 315 MHz is much longer, and probably has the rolling code. I've looked at the keyfob messages, and can't even identify a pattern of how many bits each message takes, let alone what they mean. One guess is that a message is sent incorrectly such that it fails a checksum, and then the same message is sent correctly. The receiver can separate the invalid message from the valid one by verifying the checksum. Just some intentional noise to confound decoders? do not know.

 

What we need is another key fob paired to a different Prius, to get in SKS range. What happens then?

Would a cruel prank to a Prius household be to put a non-programmed SKS fob under their car to drain the battery with failed identifications?!

 

q: If it stops polling when Ready, how does the car know if the key is removed?

 

It doesn't. It is entirely possible for you and your SO to hop in the car with the key in your pocket, get dropped off at the airport and fly to Timbuktu with the fob, and have the car keep driving. Once it's turned off though, you need the fob to lock it or start it again.

 

Try getting out of the car with the car Ready and running. The car will beep at you 3 times and display Key Not Detected on the MIF. The SKS must continue to search for the fob after being ready in order to be able to generate alarms and messages, I would think.

 

It monitors the door.

Try this:

Turn the car on with the fob in the car, window rolled down. Get out of the car and fully shut the door with the fob in the car. Wait a second or two. Then reach through the window, grab the key and leave. You can be in Timbuktu, the car will still be on, and the MFD will never complain about not having a key. Now open the driver door and shut it again. Immediately the car will complain about not seeing the fob.

I just did this in my garage.

So the system shuts down when you enter the car, and is awoken by the door opening and closing. Which makes sense and will always work unless you go dukes of hazard style. I am guessing the majority of the Prius demographic wont be doing that anytime soon though.

 

Yup. It gets much more excited about the wrong fob than the right one. Gotta drain the batteries in both the car and the fob.

 

Confirmed. The system shuts down when the car goes to Ready. When the door is opened (while in Ready), there is one blip to confirm that the key is still there. I think it checked again when I closed the door. It's really quite complicated, far more than just being ON or OFF. The trigger events seem to be detecting the key outside the car, opening the door while the key is outside, detecting the key inside the car, going to Ready, and opening the door while in Ready. I didn't check just going to IG ON (Power without the brake), or anything with the passenger door. While the doors are regularly scanned, the trunk is not scanned until the latch is pressed.