Disassemble your ELM327 cable by removing the sticker and the four screws on the enclosure. Carefully remove the circuit board.
Image: Disassembled ELM327 cable showing the circuit board.
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Before removing the OBD2 connector, mark one side with a marker to ensure correct reassembly, although removing it isn’t necessary for this modification.
Solder two wires to the TX and RX pins on the ELM327 board. Refer to the provided USB bridge chip pinout diagram for accurate pin identification. Exercise caution while soldering to avoid damaging surrounding components.
Image: Pinout diagram of the USB bridge chip on the ELM327 board.
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To identify the TX pin, program an Arduino to send data to the serial monitor with short delays. Connect a jumper wire to the Arduino’s TX pin and probe the ELM327 board. Observe the flickering surface-mounted LEDs to indicate communication. The RX pin location can be determined visually from the provided images.
Image: Soldering wires to the TX and RX pins on the ELM327 board.
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To prevent the ELM327 from communicating with your PC while connected to the Arduino, modify the USB cable. Cut the two middle wires of the 4-pin connector supplying power to the ELM327, leaving only the power lines intact. This ensures the PC only provides power, allowing the Arduino to communicate with the ELM327’s serial controller.
Reassemble the ELM327 board into its enclosure. Securing the board with tape is a viable option for convenient placement within your vehicle.
Image: Reassembled ELM327 secured with tape.
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