DIY OBDII Memory Saver for Car Battery Replacement

Maintaining your car’s settings during a battery change is crucial to avoid losing important configurations like radio presets, seat positions, and anti-theft system codes. Modern vehicles rely heavily on electronic memory, and disconnecting the battery can erase this data. For those adept with a soldering iron and seeking a practical solution, building a DIY OBDII memory saver is a straightforward project. This guide provides a step-by-step approach to create your own memory saver, ensuring your car retains its memory settings and saving you the hassle of resetting everything after a battery replacement.

Parts You’ll Need to Build Your Memory Saver

To construct this handy tool, you’ll need a few readily available components. These parts are inexpensive and can often be sourced online or from electronic component retailers:

• 12V DC 2A Mains Powered Regulated Power Supply: This will be your external power source. A reliable, regulated power supply is essential to provide a stable voltage to your car’s OBDII system.
• 16 Pin OBDII Empty Male Plug with Shell: This plug connects directly to your car’s OBDII port. You can either purchase a new plug or repurpose one from an old OBDII device.
• 2 x 470 Ohm 1/8w Resistors: These resistors are for the LEDs and help to limit the current, ensuring they operate correctly and don’t burn out.
• 1 x 3mm Green LED & 1 x 3mm Red LED: These LEDs provide visual feedback during operation. The red LED typically indicates power to the circuit, and the green LED can signal a successful connection or memory saving status.
• 3A Diode (e.g., 1N540): A diode is crucial for preventing reverse current flow into the power supply, protecting it and ensuring current flows in the correct direction to the OBDII port.

While a DC power jack socket might seem convenient for connecting the power supply, direct soldering provides a more reliable and robust connection, minimizing the risk of intermittent power loss.

Step-by-Step Guide to Using Your OBDII Memory Saver

Once you’ve assembled your memory saver, using it is a simple process. Follow these steps carefully to ensure a smooth battery replacement without memory loss:

1. Prepare Your Vehicle: Before starting, switch off all electrical consumers in your car, including lights, radio, and any accessories plugged into power outlets. This minimizes the load on the memory saver during the battery swap.
2. Access the OBDII Port: Locate your car’s OBDII diagnostic port. It’s typically found under the dashboard on the driver’s side.
3. Connect the Memory Saver: Plug the OBDII memory saver into the diagnostic socket before powering it on. At this stage, only the red LED should illuminate, indicating that it’s drawing power from the car’s battery but not yet from the external power supply.
4. Prepare for Battery Disconnection: Turn off the car’s ignition, ensure all windows and doors are closed, and avoid using the remote locking system. Keep your car keys away from the ignition to prevent accidental activation of any systems.
5. Wait for CANbus Sleep Mode: Allow approximately 5 minutes for the car’s internal systems, particularly the CANbus network, to enter sleep mode. This is essential to minimize power consumption and ensure a stable memory backup. You’ll typically notice interior and puddle lights dimming and eventually turning off, indicating sleep mode.
6. Power Up the Memory Saver: Now, connect the backup power supply to a mains socket. If correctly connected and functioning, both the red and green LEDs on your memory saver should now be lit, indicating that it’s providing external power to maintain the OBDII memory.
7. Disconnect the Old Battery: With the memory saver powered and connected, you can safely disconnect the car battery. Always disconnect the negative terminal first, followed by the positive terminal. Exercise caution to prevent short-circuiting the terminals.
8. Install the New Battery: Install the new car battery, connecting the positive terminal first, then the negative terminal. Ensure the battery clamps are securely tightened.
9. Disconnect the Memory Saver: After the new battery is installed, unplug the memory saver power supply from the mains socket. Then, open the car door and disconnect the OBDII memory saver from the diagnostic port.
10. Verify Memory Retention: Turn on the ignition. If the steering warning light does not remain illuminated, it’s a good indication that your car’s memory settings have been successfully preserved. Check your radio presets and other settings to confirm that they have been retained.

Ensuring Long-Term OBDII Memory and Avoiding Data Loss

The Duration Of Obdii Memory without power varies between vehicle models, but it is generally not designed for extended periods of disconnection. This is why a memory saver is invaluable for battery replacements. By providing a continuous, albeit temporary, power supply to the OBDII system, you effectively bypass the issue of volatile memory.

While alternative methods like using another car battery with jump leads exist, they carry risks of short circuits and unreliable connections. Mains-powered memory savers offer a safer and more consistent approach. This DIY project provides a reliable and cost-effective solution to maintain your car’s important settings, eliminating the need to reprogram systems after a battery change. Remember to always follow safety precautions when working with car batteries and electrical systems.