ELM327 OBD2 scan tool drain power problem solution


Very often elm327 Bluetooth users will discover that when the elm327 scanner will draw power supply directly from the car’s OBD port, the indicator of the scanner stays illuminates and drain your battery even the car engine is off.


The ELM327 scanners and other chipsets are designed to connect the power 5V. USB Bus power is 5V. For a few reasons though, most scanners use the constant battery line regulated to 5V instead of the 5V USB.

Possible solution:

Option 1:

1. Solder a jumper to the obdII chip and clip the vbatt line.
2. Cut the VBatt line in your obdII connector (Vehicle Side) which is pin 16. Connect Acc power. Now your OBDII reader will only run when the car is running and prevents any battery drain conditions.
3. Get an OBDII extension cable and soldier in a switch to the vbatt wire.


Option 2:

1. Use a relay to make it automatically turn on once the car is turned on.
2. Get an OBDII extension cable and hook up the power wire to the N/O (Normally open) relay contact.
3. Take a switched 12V acc power and an earth/ground wire to the coil of the relay.

Every time the car is turned on the switched 12v would power the relay coil, causing the N/O contact to “Close” allowing power to pass to the OBDII device. When the ignition is turned off the power is lost from the relay coil dropping out the contact.