No answer from A6 GSM module

Hi, I have connected an ATmega88 to a A6 GSM module. 5V power supply, RX pin on AVR to TX pin on A6. TX pin on AVR to RX pin on A6. I have programmed AVR to make a call using AT command ATD0734… and this works fine. The call is done, no problems. I have set bit rate 9600 and bit time to 104us. The problem is that there is no respons from A6 module on its TX line. Zero volts. Only sign of A6 life is when I apply 5V to it, during startup it sends some kind of pulses. But these are not 5V in amplitude, rather 1V. Could it be some electrical issue? Best regards Björn

Does your module has any regulator on board because the module operates at 4V not at 5V. If you give 5V to it, its going to keep rebooting giving over voltage warnings.
And look at the datasheet to find the right IO levels of the module. Dont connect a 5V MCU IO lines directly if the IO are not 5V tolerant