Changing your car battery can often lead to frustrating resets – radio stations forgotten, seat positions lost, and even complex systems requiring re-initialization. The solution? An Obdii Memory Saver. This nifty device provides continuous power to your vehicle’s electronics while you swap out the battery, preserving all your personalized settings and crucial computer data. If you’re a hands-on car enthusiast comfortable with basic electronics, building your own OBDII memory saver is a straightforward and rewarding project. This guide will walk you through creating a simple yet effective memory saver using readily available components.
Why Use an OBDII Memory Saver?
Modern vehicles are packed with electronic systems that rely on constant power to retain memory. When you disconnect the battery, you risk losing:
- Radio presets and security codes
- GPS navigation settings
- Seat and mirror positions
- Clock and trip computer data
- Engine and transmission control module settings
Using an OBDII memory saver prevents these headaches, ensuring a smooth battery replacement process without the need to reprogram everything.
Parts You’ll Need to Build Your OBDII Memory Saver
This DIY project requires just a few inexpensive components, most of which you might already have if you dabble in electronics:
- 12V DC Regulated Power Supply (2A): A mains-powered regulated power supply ensures a stable 12V output. You can find these online or repurpose one from old electronics.
- OBDII Male Connector (16-Pin): This plug connects to your car’s OBDII port. You can purchase a new empty plug or carefully salvage one from an old, unused OBDII diagnostic tool.
- Resistors (470 Ohm, 1/8W) x 2: These resistors are for the LEDs, limiting current and ensuring they don’t burn out.
- LEDs (3mm) – Green and Red: LEDs provide visual confirmation of power and connection status. Red typically indicates power to the circuit, and green can indicate power being supplied to the OBDII port.
- Diode (3A, e.g., 1N5400): A diode prevents reverse current flow back into the power supply, protecting it and the car’s electronics.
You’ll also need basic soldering tools, solder, and wire.
Step-by-Step Guide to Building Your OBDII Memory Saver
Follow these steps to assemble your DIY OBDII memory saver:
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Prepare the OBDII Connector: If using a salvaged connector, carefully cut the cable leaving enough wire to work with. If using a new plug, assemble the shell as per the manufacturer’s instructions.
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Wire the Circuit (Simple Configuration):
- Power Supply Connection: Identify the positive (+) and negative (-) outputs of your 12V power supply.
- Diode Installation: Connect the diode in series with the positive wire from the power supply. The banded end of the diode (cathode) should point away from the power supply and towards the OBDII connector. This ensures current flows in one direction only.
- LED and Resistor for Power Indication (Red LED): Connect a 470 Ohm resistor to the positive side of the power supply (before the diode). Connect the longer leg (anode) of the red LED to the other end of the resistor. Connect the shorter leg (cathode) of the red LED to the negative side of the power supply. This LED will light up when the power supply is plugged in.
- LED and Resistor for OBDII Connection Indication (Green LED): Connect another 470 Ohm resistor to the positive wire after the diode. Connect the longer leg (anode) of the green LED to the other end of this resistor. Connect the shorter leg (cathode) of the green LED to the negative side of the power supply. This LED will light up when power is being supplied to the OBDII port and there is a complete circuit.
- OBDII Connector Wiring: Refer to an OBDII pinout diagram (easily found online). You need to connect the positive wire (from the diode and green LED circuit) to Pin 16 (Battery Positive Voltage) on the OBDII connector. Connect the negative wire (from the power supply and LED circuits) to Pin 4 (Chassis Ground) and Pin 5 (Signal Ground) on the OBDII connector. Joining pins 4 and 5 is generally recommended for broader compatibility.
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Solder the Connections: Carefully solder all wire connections. Ensure good solder joints for reliable operation. Insulate all exposed connections with electrical tape or heat shrink tubing to prevent shorts.
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Testing: Before using it on your car, test your OBDII memory saver with a multimeter. Ensure you are getting approximately 12V at Pin 16 (positive) and ground at Pins 4 and 5 (negative) of the OBDII connector when the power supply is plugged in. The red and green LEDs should also be lit.
An OBDII port connector pinout diagram showing pin assignments, crucial for wiring your memory saver correctly.
How to Use Your OBDII Memory Saver for Battery Replacement
Using your DIY OBDII memory saver is straightforward:
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Prepare the Vehicle: Turn off all vehicle accessories – headlights, radio, interior lights, etc. Close all doors and windows.
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Connect the Memory Saver: Locate your vehicle’s OBDII port (typically under the dashboard on the driver’s side). Plug in your OBDII memory saver, but do not yet plug in the power supply to the mains. Only the red LED should be lit at this stage, indicating the circuit is powered up to that point.
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Allow Vehicle to Enter Sleep Mode: Turn off the ignition and remove the keys. Wait for approximately 5 minutes to allow the car’s computer systems to fully shut down and enter sleep mode. This minimizes power draw during battery replacement. Interior and puddle lights should dim off.
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Power Up the Memory Saver: Plug the power supply of your OBDII memory saver into a mains socket. Both the red and green LEDs should now be illuminated, indicating power is being supplied to the car’s OBDII port.
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Disconnect and Replace the Battery: Carefully disconnect the old car battery terminals, starting with the negative terminal first, then the positive. Remove the battery. Install the new battery, connecting the positive terminal first, then the negative. Crucially, avoid shorting the battery terminals together during this process, as this could interrupt the memory saver’s power supply and defeat its purpose.
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Disconnect the Memory Saver: Once the new battery is securely installed, unplug the OBDII memory saver power supply from the mains first, then unplug the OBDII connector from your car.
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Verify Settings: Start your vehicle and check if your radio presets, seat positions, and other settings have been preserved. If the steering warning light does not remain illuminated, your memory settings should be intact.
A completed DIY OBDII memory saver, showcasing the simple circuit and connections within the OBDII plug.
Important Considerations and Safety Tips
- Polarity: Double-check the polarity of your power supply and LED connections. Incorrect polarity can damage components.
- Current Rating: Ensure your power supply provides at least 2A. While the car draws minimal current in sleep mode, a sufficient rating ensures stable power.
- Fuse Protection (Optional but Recommended): For added safety, you could incorporate a 2A fuse in series with the positive lead, although this design omits it relying on the power supply’s protection.
- Alternative Power Sources: While this guide focuses on a mains power supply, you could theoretically use a spare car battery as a power source. However, this introduces risks of short circuits if not handled carefully and fused appropriately. Mains power is generally safer and more convenient for home use.
- Vehicle Compatibility: OBDII memory savers are compatible with most modern vehicles equipped with an OBDII port, which has been standard since the mid-1990s. However, always consult your vehicle’s manual if you are unsure.
Conclusion
Building your own OBDII memory saver is a satisfying and practical DIY project that can save you time and frustration during car battery replacements. By following this guide, you can create a reliable tool to preserve your vehicle’s memory settings and enjoy hassle-free battery changes. This simple device is a valuable addition to any DIY car enthusiast’s toolkit.
