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Autosteer Nag Killer

Suppresses the Autopilot "hands on wheel" nag on Tesla vehicles using the same method as the Chinese TSL6P commercial module (~200 EUR), replicated on a ~15 EUR ESP32 board.

Difference from ISA Speed Chime
  • Nag Suppression (ISA Speed Chime): Modifies CAN 39F message (controls speed chime alerts)
  • Autosteer Nag Killer: Modifies CAN 880 message (suppresses "hands on wheel" nag)

These are two different features addressing different nag/chime issues.

How It Works​

The module echoes CAN 880 (EPAS3P_sysStatus) frames with a modified payload:

  1. Listens for CAN 880 frames where handsOnLevel = 0 (driver hands not detected)
  2. Immediately retransmits the frame with:
    • byte 3 = 0xB6 → fixed torsionBarTorque = 1.80 Nm
    • byte 4 |= 0x40 → handsOnLevel = 1
    • byte 6 counter + 1 → next expected counter value
    • byte 7 → recalculated checksum: (sum(byte0..byte6) + 0x73) & 0xFF
  3. The real EPAS frame with the same counter arrives after ours → receiver rejects it as duplicate
  4. When driver applies real steering torque (handsOn >= 1), the module does nothing

Frame Example​

Real EPAS:      12 00 08 23 1F 89 4C A4   (ho=0, torque=+0.33Nm, cnt=C)
Our modified:   12 00 08 B6 5F 89 4D 78   (ho=1, torque=+1.80Nm, cnt=D)

Tested Hardware​

VehicleHWAutopilotStatus
Model Y Performance 2022HW3Basic AutopilotWorking

Supported Boards​

Any ESP32 board with a CAN transceiver will work. Tested with:

  • LILYGO T-CAN485 (~15 EUR) — ESP32 + SN65HVD230 CAN transceiver, screw terminals

Other compatible boards:

  • ESP32 + MCP2551 or SN65HVD230 breakout
  • M5Stack ATOM CAN
  • Any board supported by this project

Wiring to Vehicle​

Connect to X179 diagnostic connector, pin 2 and pin 3 (CAN bus 4):

Board CAN_H  ──────  X179 Pin 2  (CAN bus 4+)
Board CAN_L  ──────  X179 Pin 3  (CAN bus 4-)
Board USB    ──────  Any 5V source (car USB, phone charger, laptop)

X179 20-pin Connector Pinout (S/X new Blue / Model Y)​

     ┌─────────────────────────────┐
     │  1   2   3   4   5   6   7  │  ← Top row (pin 1 = 12V+)
     │  8   9  10  11  12  13  14  │  ← Middle row
     │ 15  16  17  18  19  20      │  ← Bottom row (pin 20 = GND)
     └─────────────────────────────┘
            (front mating face)
PinFunctionNotes
112V+Vehicle power
2CAN bus 4+← Connect CAN_H here
3CAN bus 4-← Connect CAN_L here
6K/Serial
9CAN bus 2+Vehicle CAN
10CAN bus 2-Vehicle CAN
13CAN bus 6+Body/Left CAN (used by FSD mod / Enhance cable)
14CAN bus 6-Body/Left CAN
18CAN bus 3+Chassis CAN
19CAN bus 3-Chassis CAN
20Ground
Important: CAN Bus 4 Only

The nag killer works ONLY on CAN bus 4 (pin 2/3). It does NOT work on CAN bus 3 (pin 18/19) or CAN bus 6 (pin 13/14) due to Tesla's anti-spoofing on those buses.

Pin numbering: Always read pin numbers from the FRONT MATING FACE of the connector. If you look at the back (wire side) of a female connector, the numbers appear mirrored!

Building & Flashing​

For LILYGO T-CAN485:

pio run -e lilygo_tcan485_nag_killer
pio run -e lilygo_tcan485_nag_killer -t upload

For generic ESP32 + CAN transceiver (default pins GPIO 5/4):

pio run -e esp32_twai_nag_killer
pio run -e esp32_twai_nag_killer -t upload

With Arduino IDE / CLI​

Use build flag -DNAG_KILLER and set your board's TX/RX pins with -DTWAI_TX_PIN=GPIO_NUM_xx -DTWAI_RX_PIN=GPIO_NUM_xx.

LILYGO T-CAN485 Pin Mapping​

FunctionGPIO
CAN TX27
CAN RX26
5V Enable16
CAN Standby23 (LOW = active)

What Doesn't Work (Extensively Tested)​

ApproachBusWhy it fails
CAN 880 echoBus 3 (Chassis, pin 18/19)Gateway anti-spoofing blocks
CAN 880 echoBus 6 (Body, pin 13/14)DAS ignores injected frames
CAN 82 echoBus 6 (Body, pin 13/14)DAS ignores
CAN 905 echoBus 3 (Chassis)Source validation rejects
CAN 1160 LKA torqueBus 3 (Chassis)DAS sends at 50Hz, overrides
CAN 82 injectionBus 3 (Chassis)No effect

Only CAN bus 4 (pin 2/3) works — it does not have the same counter/source validation as the other buses.

Safety​

Safety Guidelines
  • The module only activates when handsOnLevel = 0 (hands not detected)
  • When you grip the wheel normally, the module does nothing
  • CAN bus-off auto-recovery is built in
  • No vehicle modifications — fully reversible, plug and play
  • Keep your hands near the wheel and stay attentive at all times

Credits​

  • Reverse engineered by BatteryPlug (nicolozak) with Claude AI assistance
  • TSL6P method decoded with help from the Tesla Open CAN Mod Discord community
  • DBC files from Tesla community (Poppyseed, Onyx)