This is a guide for how to swap the electronic power steering motor on a TSS-P (2016-2020) Prius with one from a TSS2 Prius (2021-2022). This raises the torque limit, upgrades the steering position encoder, and provides more stable lateral control for the Comma. From my experience, the torque increases from ~45° to ~135°. This enables the Comma to take some right and left turns at intersections. Below is an example of the new torque around a corner running Sunnypilot with MADS enabled.
The two motor part numbers to get are: 89650-47600 or 89650-47800. 2021-2022 C-HR motors may also work, but are untested. Try searching on eBay or junkyards for used motors. Learning eBay search syntax such as (21, 22, 2021, 2022) Prius (EPS, power steering) and saving searches with notifications helps. New parts are also an option, but may cost up to 8x more. Make sure there is a clear picture of the part number on top and check the VIN for a 2021-2022 Prius.
Only the highlighted portion of the part is needed, which can easily be removed by unscrewing the two 14mm bolts.
- 10, 12, & 14mm wrenches with extensions
- Phillips head screwdriver
- Bungee cord or prybar to keep steering wheel up
- Trim removal kit (optional)
- Breaker bar for tight bolts (optional)
Replacing the cogwheel inside the motor housing with a solid 3D-printed one can reduce actuator delay from 0.3s down to 0.12s. This will make it slightly harder to install the new motor, however, as it is a tight fit. If doing this mod, print using PETG with 100% infill. Do a test fit with the new motor and grease both sides of the cogwheel.
Before disconnecting the battery, push the driver seat back and make any power adjustments. The driver seat can also be entirely removed for easier access, but is not neccessary. The battery should be disconnected because the knee airbag needs to be removed. Disconnect the negative terminal of the 12V battery in the hood with the 10mm. Put a non-conductive material in between the screw and the terminal like a towel to prevent an accidental connection.
Start by removing the plastic trim pieces by the door. This will allow easier access to the other components. The plastic trim pieces usually just include clips that can be just pulled by hand or with a trim removal tool. Remove the trim on the side of the dash and on the edge of the door.
Then, remove the trim on the left of the footwell by unscrewing the plastic screw by hand and pulling the trim off.
Next, remove the trim above the footwell by unscrewing the two Phillips screws, disconnecting the white LED cable, and tugging down. These types of cables will be seen everywhere and can be disconnected by pushing down on the small tab and pulling.
Remove the lower trim with the hood popper by disconnecting the cables behind it, through the opening on the side of the dashboard. The hood popper can optionally be removed by pushing in the highlighted portion of the connector.
The driver side of the trim should now look like this:
Next up, the knee airbag needs to be removed. To do this, unscrew the two 10mm bolts on the left and the right.
To disconnect the airbag connector, simply pop the black clip back.
The next steps will be in preparation for dropping the steering column to access the EPS motor. Rotate the steering wheel (will be tight due to no power) until a Phillips screw is visible on the right or left. Unscrew this and do the same for the other side.
Separate the top and bottom plastic trims of the steering wheel. The steering wheel wiring harness can also be disconnected to prevent the cables from stretching when dropping the column.
Now, the footwell air vent needs to be moved out of the way to make room for the steering column. Remove the highlighted 12mm bolt on the top left side of the air vent.
Split apart the air vent by popping apart the plastic tabs along the bottom. Then, move it back behind the brake pedal, out of the way of the steering column.
The steering column pivot bolt acts like a hinge towards the lower part of the column. In order to access it, the brake pedal light switch towards the left may need to be removed.
Remove this gray switch by simply disconnecting the black connector and twisting the switch in place. Make sure to note how much the blue button is displaced when reinstalling.
Now, the 14mm pivot bolt can be removed and the bottom of the column dropped down.
The final step before dropping the entire steering column is removing the two 14mm bolts in line with the steering adjustment lever. Before removing, make sure to hook a bungee cord around the steering column so it doesn't drop too far. Extending the steering wheel out and propping it on the seat or with another item could also work.
Carefully drop down the column while it is supported and locate the old EPS motor. Rotating and moving the column could help to get better access to the motor. Remove the two 12mm bolts and unclip the three black connectors.
It may take a couple of tries lining up the jaw coupler of the new motor onto the base, so be patient. It will be a tight fit if the solid cogwheel mod is used.
Finally, just reverse these directions to put everything back in place. Getting someone to hold up or propping up the steering column while putting back the bolts will be helpful as it is heavy. Once everything is back together, the Comma should recognize the new motor immediately with no code changes. You might see an "ICS malfunction" error when reconnecting the 12V battery, but this should go away on its own after a couple of minutes.
Feel free to message me (@vishbk) on Discord with any questions. Erich also has made a great video on replacing his Prius Prime EPS motor.