Audi A3 8V, European market, EA888 Gen 3 1.8 TFSI, engine code CJSA. Original ECU is a Simos 12.1.

The Simos 18.1 has better tuning tool support, more boost control options, and a large community around patches and calibration. bri3d's open-source toolchain (TC1791_CAN_BSL, Simos18_SBOOT, VW_Flash) enables full bench read/write without commercial tools. The Simos 18.1 is a direct plug & play swap for the 12.1 on EA888 Gen 3 — same connector, same sensors, no wiring changes.

If you don't have access to ODIS Engineering, you need an immo-off patched binary since the replacement ECU is married to a different vehicle. You can patch it with my Tune Editor or Bin Toolz by Switchleg1.

I used 8V0906264H__0003 as its the best supported version for the europe CJSA.

The following part numbers are listed in the VW_Flash update matrix for the 1.8T: 8V0906264A, 8V0906264D, 8V0906264F, 8V0906264K, 8V0906264L, 8V0906264M. This guide was done with an 8V0906264D.

• Raspberry Pi 5
• Waveshare 2-CH CAN FD HAT
• ESP32 WROOM-32
• 3.3V ↔ 5V bidirectional level shifter
• 12V bench power supply (at 13.3V the ECU never drew more than 0.7A, so a small supply works)
• Simos 18.1 ECU

You have to open the ECU and solder a few connections. Refer to the images in bri3d/TC1791_CAN_BSL:

Board1.jpg: Connect red → 1kΩ resistor → black + yellow.

Board3.jpg: Connect turquoise and white.

Board2.jpg: Wire directly to Pi GPIO 27.

RST.jpg: Wire directly to Pi GPIO 22.

3V3 for the level shifter LV side comes from the Pi's 3.3V pin.

The HWCFG pullup wires on the PCB can come loose — if you get no CAN response after reset, check your solder joints first.

ESP32 GND, Pi GND, CAN HAT G pin, ECU GND, level shifter GND, and 12V supply GND all need to be tied together. Missing CAN ground was a major issue during this build — without a shared ground reference, CAN communication drops out intermittently or completely.

Your desk may look like that.

Enable SPI via sudo raspi-config.

Add to /boot/firmware/config.txt:

dtparam=spi=on
dtoverlay=spi1-3cs
dtoverlay=mcp251xfd,spi0-0,interrupt=25
dtoverlay=mcp251xfd,spi1-0,interrupt=24

Reboot. Then bring up CAN:

sudo ip link set can0 up type can bitrate 500000
sudo ifconfig can0 txqueuelen 65536

Verify with candump can0 (from can-utils) — you should see ECU traffic when the ECU is powered.

cd ~
git clone https://github.com/bri3d/TC1791_CAN_BSL
git clone https://github.com/bri3d/Simos18_SBOOT
git clone https://github.com/bri3d/VW_Flash

cd ~/Simos18_SBOOT
gcc twister.c -o twister -O3 -march=native -fopenmp -lgmp

You may need to install libgmp-dev and libgomp1 if they're not already present.

cd ~/TC1791_CAN_BSL
uv pip install python-can tqdm udsoncan==1.21 "can-isotp<2.0" lz4

can-isotp must be below 2.0. Version 2.x changed the socket API and breaks both TC1791_CAN_BSL and VW_Flash.

cd ~/VW_Flash

# Remove wxPython from dependencies — it's only for the GUI and takes forever to build on ARM
sed -i '/wxpython/Id' pyproject.toml requirements.txt 2>/dev/null

# Compile LZSS
cd lib/lzss
gcc -O2 -o lzss lzss.c
cd ../..

uv pip install -r requirements.txt
uv pip install "can-isotp<2.0"

The Pi 5 uses the RP1 chip for GPIO. pigpio (the DMA-based timing library used in bri3d's original scripts) does not work on the Pi 5. Software PWM has too much jitter for reliable SBOOT entry. The ESP32 has dedicated hardware timers and provides jitter-free PWM at 3.2kHz.

The Tricore GPTA comparator measures two signals:

• Signal 1 (ECU Pin 71): 3.2kHz, 50% duty cycle
• Signal 2 (ECU Pin 66): 3.2kHz, 25% duty cycle, 270° phase offset

Flash to ESP32 via Arduino IDE. Board: ESP32 Dev Module.

#include "soc/gpio_struct.h"
#include "driver/gpio.h"
#include "esp_timer.h"

#define PIN_SIG1  18  // 50% duty → ECU Pin 71
#define PIN_SIG2  19  // 25% duty → ECU Pin 66

// 3200 Hz = 312.5µs period
// t=0:     Sig1=HIGH, Sig2=LOW
// t=156:   Sig1=LOW
// t=234:   Sig2=HIGH
// t=312:   Sig2=LOW → next cycle

void pwmTask(void *param) {
  gpio_set_direction((gpio_num_t)PIN_SIG1, GPIO_MODE_OUTPUT);
  gpio_set_direction((gpio_num_t)PIN_SIG2, GPIO_MODE_OUTPUT);

  int64_t cycle_start;

  while(1) {
    cycle_start = esp_timer_get_time();

    GPIO.out_w1ts = (1 << PIN_SIG1);
    GPIO.out_w1tc = (1 << PIN_SIG2);

    while(esp_timer_get_time() - cycle_start < 156);
    GPIO.out_w1tc = (1 << PIN_SIG1);

    while(esp_timer_get_time() - cycle_start < 234);
    GPIO.out_w1ts = (1 << PIN_SIG2);

    while(esp_timer_get_time() - cycle_start < 312);
  }
}

void setup() {
  Serial.begin(115200);
  xTaskCreatePinnedToCore(pwmTask, "PWM", 2048, NULL, configMAX_PRIORITIES - 1, NULL, 1);
  Serial.println("PWM 3200Hz running on Core 1");
}

void loop() {
  delay(1000);
}

Measure DC voltage with a multimeter (Hz mode won't work at 3.2kHz on cheap meters):

• GPIO 18: ~1.65V (50% of 3.3V)
• GPIO 19: ~0.825V (25% of 3.3V)

The ESP32 runs PWM continuously once powered via USB. No communication with the Pi needed.

Since pigpio doesn't work on the Pi 5, the GPIO control in bootloader.py needs to be adapted. The PWM generation is handled entirely by the ESP32, so the Pi only needs to control the reset and HWCFG pins.

Pin assignments differ from the original because of CAN HAT conflicts:

• Reset: GPIO 22 (original was 23)
• BOOT_CFG: GPIO 27 (original was 24)

The sboot_pwm() function should do nothing since the ESP32 handles PWM:

def sboot_pwm():
    print("PWM handled by ESP32 (external)")
    return type('', (), {'cancel': lambda self: None})()

Set CRC_DELAY = 0.001 — the Pi 5 is faster than the Pi 3B+ and the default 0.0005 is too short. If the CRC value comes back as 0x0, the delay is too small. If the CRC address jumps multiple iterations past the target, the delay is too large. You want exactly one iteration (start_address + 0x100).

cd ~/TC1791_CAN_BSL
uv run bootloader.py

(BSL) extract_boot_passwords

This enters SBOOT 4 times via PWM break-in, cracks the Seed/Key each time, captures CRC values, and calculates boot passwords.

Each round should show:

CRC Address Reached:
0x8001430c          ← start + 0x100, exactly one iteration
CRC32 Current Value:
0xa980571e          ← not 0x0

Final output:

39a9485b5b3f95b5d6419bd3ddc97f92

First 16 hex chars = Read passwords: 39a9485b 5b3f95b5 Last 16 hex chars = Write passwords: d6419bd3 ddc97f92

These are permanent, burned into OTP during manufacturing.

(BSL) upload
(BSL) send_read_passwords 39a9485b 5b3f95b5
(BSL) flashinfo

Check that "Flash Locked Error" shows DISABLED. If still ENABLED, your CRC_DELAY may be wrong.

(BSL) dumpmem AF000000 18000 PMU0_DFlash.bin
(BSL) dumpmem AF080000 18000 PMU1_DFlash.bin
(BSL) dumpmem 80000000 200000 PMU0_PFlash.bin
(BSL) dumpmem 80800000 100000 PMU1_PFlash.bin

Back these up.

You can patch it with my Tune Editor or Bin Toolz by Switchleg1.

This bypasses the immobilizer and gets the ECU into a state where VW_Flash can communicate via UDS.

(BSL) upload
(BSL) send_write_passwords d6419bd3 ddc97f92
(BSL) erase_sector 80800000
(BSL) reset

The ECU will now boot into CBOOT since ASW3 is erased and the application software can't start. Disconnect the BSL wires (RST, HWCFG). Leave only CAN H/L/G + 12V connected.

cd ~/VW_Flash
uv run VW_Flash.py --action flash_unlock --frf FL_8V0906259H__0001.frf

uv run VW_Flash.py --action flash_bin \
  --input_bin ./8V0906264H__0003_immo_off.bin \
  --patch_cboot

--patch_cboot patches the Customer Bootloader to accept modified software blocks.

uv run VW_Flash.py --action get_ecu_info

You should see your part number, software version, and State Of Flash Memory: 00.

The ECU will have the donor vehicle's VIN. This causes a gateway DTC for VIN mismatch and is TÜV-relevant.

The VIN is stored in encrypted DFlash — you can't hex-edit it. The VIN mismatch doesn't prevent the engine from starting with immo-off.

No CAN traffic: Check 12V, CAN H/L, and especially the CAN ground (HAT G pin to ECU). Run candump can0. If ip link show can0 shows state DOWN, restart CAN.

None responses after reset: Loose HWCFG pullup wire on the ECU PCB. Resolder.

FAILURE / 0x0A7 messages (ECU boots normally): PWM signals not reaching the ECU. This is what the ESP32 solves — Pi 5 software PWM doesn't cut it. Also try swapping the Pin 66/71 connections.

CRC Value = 0x0: CRC_DELAY too small. Increase it.

CRC Address too high: CRC_DELAY too large. Decrease it.

socket.bind() got an unexpected keyword argument 'rxid': Wrong can-isotp version. uv pip install "can-isotp<2.0".

• bri3d — TC1791_CAN_BSL, Simos18_SBOOT, VW_Flash
• resilar/crchack — CRC reversal