iBooster Brake Retrofit#
The Bosch iBooster is an electromechanical brake booster that replaces the vacuum-based braking system found in pre-AP Tesla Model S vehicles. This retrofit enables full electronic brake control through openpilot, giving you stop-and-go capability and automatic emergency braking (AEB).
Why do pre-AP cars need this?#
Pre-AP Model S vehicles (built before October 2014) use a traditional vacuum brake booster. Since there is no electronic control over the friction brakes, openpilot can only slow the car using regenerative braking via the comma pedal. Regen braking has significant limitations:
- Only works above ~5 MPH — it cannot bring the car to a full stop
- Limited deceleration force — not enough for sudden slowdowns
- No automatic emergency braking possible
- The driver must always be ready to manually brake
When Tesla introduced AP1 hardware in late 2014, they switched to the Bosch iBooster, which is what enables electronic braking on all newer Teslas.
What does the iBooster add over the comma pedal?#
| Comma Pedal only | Comma Pedal + iBooster | |
|---|---|---|
| Speed control range | 1–18+ MPH (acceleration only) | 0–18+ MPH (full stop-and-go) |
| Braking method | Regenerative braking only | Regen + friction brakes |
| Minimum speed | ~5 MPH (regen cuts out below this) | 0 MPH (full stop) |
| Emergency braking | Not possible — driver must brake | AEB available through openpilot |
| Braking force | Limited by regen capability | Full hydraulic braking |
In short: the comma pedal gives you acceleration control, while the iBooster adds full braking control. Together they provide complete longitudinal control of the vehicle.
How it works#
The Bosch iBooster is a vacuum-independent, electromechanical brake booster:
- An electric motor drives a three-stage gear unit that generates boost force
- That force is converted into hydraulic brake pressure via the master cylinder
- It can build full braking pressure in approximately 120 milliseconds
- Pedal feel remains completely normal to the driver
The iBooster communicates over CAN bus. An iBooster controller ECU (such as the one made by SGH Innovations) acts as the interface between openpilot’s CAN commands and the iBooster.
Safety#
- Failsafe mode: If CAN bus communication is lost, the iBooster falls back to reading the physical brake pedal sensor directly — the driver always retains full manual braking
- Mechanical backup: If the motor fails entirely, direct hydraulic braking through the pedal is still available
- Pressure limit: The openpilot implementation caps iBooster travel to prevent excessive braking commands
- Accelerator interlock: Brake commands are suppressed when the accelerator pedal is physically pressed
Parts needed#
- Bosch iBooster Gen 1 unit — sourced from a salvage AP1 Tesla Model S or Model X (part #1037123-00-A or -00-B)
- iBooster controller ECU + wiring harness — interfaces between openpilot and the iBooster CAN protocol
- ABS/ESP module upgrade — the pre-AP ABS module is not compatible with the iBooster
- Wheel speed sensors — all four need to be replaced with AP-compatible units
- Comma pedal — still required for acceleration control
The iBooster physically replaces the vacuum brake booster, vacuum pump, vacuum reservoir, and associated piping.
Installation#
This is a significant mechanical and electrical undertaking:
- Requires removing the old vacuum brake system and installing the iBooster in its place
- Brake lines must be flushed
- The iBooster connects to two CAN buses and requires a 40A fused 12V power supply
- Approximate parts cost: $800–$1,000 USD
This retrofit is only relevant for pre-AP Tesla Model S vehicles. All AP1 and newer Teslas already have the iBooster from the factory.