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Troubleshooting

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github-actions[bot] edited this page May 28, 2026 · 3 revisions

Troubleshooting

Display is blank or unresponsive

  • Check SDA/SCL wiring (A4/A5 on the Uno).
  • Confirm the I2C address. The default is 0x3C; some SH1107 modules ship with 0x3D. Update OLED_I2C_ADDR in src/display/Display.h and reflash.
  • Run the i2c_scanner_sketch.ino from the docs/ folder to confirm the address.

ECU does not respond / connection fails immediately

  • Ignition must be ON (engine does not need to be running).
  • Verify the baud rate. Most VAG K-Line ECUs from ~1998–2006 use 10400 baud. Try each rate from the setup menu.
  • Double-check the K-Line wiring polarity — FT232 TXD → Arduino pin 3, FT232 RXD → Arduino pin 2.
  • Confirm PCB traces were cut after soldering to the FT232 (see Hardware Setup).
  • Use the debug build to read event codes from dbg_monitor.py:
    • KWP_SYNC_FAIL or KWP_SYNC_MISMATCH — K-Line signal not reaching the Arduino, or wrong polarity.
    • KWP_TIMEOUT with val = 0 — no bytes received at all; check wiring and power.
    • KWP_TIMEOUT with val > 0 — partial response; ECU address may be wrong.

ECU connects then drops / keepalive failures

  • KWP_KEEPALIVE_TX or KWP_KEEPALIVE_RX in the debug log indicates the ECU is timing out between blocks.
  • The cooperative task scheduler is tuned to keep the OBD communication cycle well within typical ECU timeout windows. If this occurs only under load, check that the display update loop is not blocking.
  • Power supply instability can cause intermittent disconnects — try a dedicated USB power bank.

Stale or incorrect sensor values

  • Confirm the ECU address and measurement group mapping for your specific ECU. The default mapping targets the instruments cluster (0x17) of a 1J platform VW with a Marelli 1.6 16V engine ECU (0x01). Other ECUs have different group contents.
  • Use a VCDS or equivalent KWP tool to record raw group data and compare against what KWPSensorDecode.cpp expects.
  • In simulation mode (SIM at startup) the firmware generates synthetic signals — connect to ECU mode for real data.

Flash too full

  • Production build (pio run -e uno) fits at ~96% flash. The debug build (uno_debug) reaches 100% on the standard Uno.
  • If you add features, monitor pio run output for flash/RAM percentages. RAM overflows cause silent crashes.
  • Disable OBD_EXPERIMENTAL_SCREENS if not needed — it saves meaningful flash.

Upload fails / avrdude errors

  • Check the port name: /dev/ttyUSB0 (Linux), COM3 (Windows), /dev/cu.usbmodem* (macOS).
  • On Linux, add your user to the dialout (or uucp on Arch) group and log out/in.
  • The 115200 baud rate used by pio run --target upload must match the Arduino Uno bootloader. Do not change it.

Button press not registering

  • Buttons use INPUT_PULLUP; they must connect pin to GND (not 5V).
  • The 50 ms debounce or 222 ms SELECT timeout may absorb very short presses. Hold buttons slightly longer if inputs are being dropped.
  • Auto-repeat fires on UP/DOWN/LEFT/RIGHT after the repeat threshold — this is intentional for fast menu scrolling.

ECU emulator connection issues

When using OBDisplay-Emu for bench testing, ensure the emulator is in ECU mode and that SIM mode is not selected on OBDisplay at startup. SIM mode generates local synthetic data and never talks to the serial port.

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