Portable OBDII Memory Saver

Tired of losing ECU and radio memory when I replace the car battery myself, I followed the instructions in this video and made my own ODBII memory saver.

The gadget is extremely simple to make. I ordered the ODBII plug and A23 battery holder. The diode could be any small signal diode that you have around the toolbox (I am using 1N4148).

Then simply solder:

Battery holder GND => pins 4, 5 on OBDII
Battery holder VCC => diode (+)
Diode (-) => pin 16 on OBDII

That's it. Stuff the battery holder into the empty part of the shell and reassemble. I didn't even bother to screw the shell together.

You can check by inserting a battery and measuring the voltage across pin 4/5 and pin 16. It should be around 12.6V (for a fresh A23 battery) - 0.4V ~= 12.2V. Anything above 11V should work well enough to keep the ECU and radio memory while inserted.

To use, first insert the memory saver into the OBDII port in the car. Then remove the car battery and perform the battery replacement. Finally remove the memory saver.

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