I am using Arduino Uno and HC05 Zs-040 Bluetooth module to establish a connection with ELM327 mini OBDII Bluetooth adaptor.

I have tried more than 15 different sequences of AT commands and most of them works successfully and HC05 reply with "ok" with no errors.

When I switch off the power from the HC05 and reconnect it again to connect automatically to the MAC address stored in it during configuration, the HC05 connects to the ELM327 OBDII adaptor for a time interval ranges from 2 to 5 seconds then the connection is lost.

I was able to notice that from the LED blinking on the HC05. This process of connection and disconnection is repeated automatically and the LED on the HC05 blinks in different patterns.

Also, I was able to connect to the ELM327 OBDII adaptor using a python script and it connects to it (I did that at the same time when the HC05 was trying to connect to OBDII adaptor which confirms that the connection between HC05 and the adaptor was not established).

In addition, I was able to connect to ELM 327 adaptor using Torque application and Bluetooth terminal application and both work fine.

Can anyone help me figuring out why does the connection is lost as soon as it is established?

1 Answer 1


I faced a similar problem when working with HC-05 module with an Android terminal application and connection was lost after some time and many it was just not able to connect. Upon some hit and trials I found that it was just an power issue with HC-05 and as soon as I tried it out by reducing load on HC-05 by connecting it alone on 5V supply from Arduino and switching others to a 3V supply it worked like butter and I didn't faced any problem till now.

This worked for me try this out.

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