M66 module doesn't restart


my M66 module sometime falls into state, where I can’t restart it from.

After 10 x sending AT to M66 without response, I try to restart module - see picture
Pull PWRKEY pin for 870ms down, then wait 13 sec and try to switch on.

However VDDEXT voltage doesn’t change, no NORMAL POWERDOWN on serial line appears.

Communication with modem is stuck, and only way how to fix is power down / power up.

However netlight pin stil shows that modem is attached to GSM network.
Any idea?

Many thanks

Dear Radomir Kozub,
Thanks for your inquiry in Quectel forum.
You mean you cannnot restart the module with PWRKEY pin ? Could you double check the following Timing of resetting system? Normally, you should make sure it have the 500ms delay before resetting the module. And you also can try to use AT+CFUN=1,1 to reset the module. Thanks!

Yes, M66 modem doesn’t switch off by PWRKEY pulse, as on picture in original post.

In the documentation, width of pulldown pulse on PWRKEY should be 0,7 to 1sec.
Pulse on picture (in my design) is 0,873sec, so it is compliant with doc.

However, module doesn’t switch off.

Any idea?


Dear Radomir,
I have checked in my side, please check the following test log. When i press PWRKEY to turn off the module, it can report “NORMAL POWER DOWN” normally, then waiting more than 500 ms to turn on module again. The process is quite normal, have no any question. So please check the whole process in your side. Thanks!


yes, if modem operates correctly, it goes the same way as you have in your log.

However in my case modem doesn’t respond on serial line, so no output data on modem TX line is printed,
and can’t be switched off both ways, AT+CFUN or PWRKEY


If that, it is better to change another module to have a try. Thanks!
Just as i have test in my side, the method is correct. Thanks!