I have had obd2 codes that appear with check engine light ONLY WHEN TRANSMITTING. They go away and do not reappear after a couple of drive cycles with no use of HF. It only happens on 20 meters . Not on 40 80 or 10. The last one was a LDE code. My friend at gas station checked it free and found no problem. He says he sees random codes appear sometimes and never sees them return or they do and a bad part or such is found. As I said only on 20 meters .