Short version: There is a device you can buy from China for about $125 that hacks Adaptive Cruise Control to work down to 0mph - i.e. stop and go. The device is called a Smart DSU.
Long version: The OpenPilot community developed a device to help Toyotas with TSS-P allow an OpenPilot device to better control the acceleration and braking without disabling AEB. On Toyota Siennas with TSS-P, it just so happens that this device has the added benefit of enabling the stock ACC to work down to 0mph. So, when following another car that stops, ACC with a Smart DSU will brake all the way to a stop and resume when the other car resumes. (Note: You still cannot set the speed to below 28 mph and you still cannot engage radar cruise until you reach 28 mph. Also, if you tap the brake at all while below 28mph, it disengages and you cannot re-engage until you reach 28mph again.)
Up until recently, the only way to get an S-DSU buy the parts and build one yourself or chat with one particular user on the comma.ai discord server and get in line to pay him $150. But, now there is a seller in China (on Taobao) that sells them.
This Chinese Smart-DSU is a like a dongle that sits in between the Toyota DSU and the car. To install it, you unplug the stock DSU, plug the "smartener" into the stock DSU, and plug the cars harness into the SDSU. I had to lay down on the passenger-side floor to get to it. It's a bit awkward to reach, but it only took a few minutes and required no tools.
Of course there are many issues that makes this a very risky thing to do. These are just some of them:
Or, buy from this agent: Superbuy-Shopping Agent
Long version: The OpenPilot community developed a device to help Toyotas with TSS-P allow an OpenPilot device to better control the acceleration and braking without disabling AEB. On Toyota Siennas with TSS-P, it just so happens that this device has the added benefit of enabling the stock ACC to work down to 0mph. So, when following another car that stops, ACC with a Smart DSU will brake all the way to a stop and resume when the other car resumes. (Note: You still cannot set the speed to below 28 mph and you still cannot engage radar cruise until you reach 28 mph. Also, if you tap the brake at all while below 28mph, it disengages and you cannot re-engage until you reach 28mph again.)
Up until recently, the only way to get an S-DSU buy the parts and build one yourself or chat with one particular user on the comma.ai discord server and get in line to pay him $150. But, now there is a seller in China (on Taobao) that sells them.
This Chinese Smart-DSU is a like a dongle that sits in between the Toyota DSU and the car. To install it, you unplug the stock DSU, plug the "smartener" into the stock DSU, and plug the cars harness into the SDSU. I had to lay down on the passenger-side floor to get to it. It's a bit awkward to reach, but it only took a few minutes and required no tools.
Of course there are many issues that makes this a very risky thing to do. These are just some of them:
- You'd be hacking some core safety features of your car. Are you nuts? Seriously, don't do this. It could lead to serious injury or death.
- There could be serious liability issues. Who knows what your insurance company would say about an accident that had anything to do with TSS-P's safety features with this installed.
- You're buying from some place in China on Taobao. There's pretty much no warranty and no support.
- Buying from Taobao is a total PITA. Using an agent like Superbuy adds a small fee but is much easier, but it's still a pain.
- TSS-P ACC doesn't always recognize cars that are completely stopped. You could get accustomed to using it and then, one day, it could plow into back of a bunch of cars at a stoplight. Of course, stock ACC could do this without this device.
- I can only confirm this seems to work works well on my 2018 Sienna, but I haven't tested it extensively. It should probably work just as well on 2019-2020 Siennas, but I can't confirm that.
Or, buy from this agent: Superbuy-Shopping Agent