There could be various reasons for the occurrence of HP fax error 388, and the primary one includes sudden shutdown due to power off or malware attack. You can see this when you are trying to send the fax on a disrupted line. To know the troubleshooting steps, you can print the fax test. To get the report turn on your fax machine and then click the setup button, now navigate to the service option you can use the arrow button to scroll and then click Ok. The next step is to locate the option Run fax test and press the Ok button. Now, wait for the test report to print, which includes the troubleshooting steps to get rid of HP fax error 388.