So, on this 91 Civic 1.5, I checked the ECU flashes 4 different times just in case my ability to count has degraded with age, and even had another Mech check it. Yup, 1 flash, break, followed by 8 flashes. repeat. Check Engine light goes away after engine shut down, but reappears after start up and a couple of miles, where it remains until shutdown. I have 4 code lists and all skip from 17 to 19. Any ideas anyone? Is this what they call a soft code, one that hasn't set yet?

 

You have two codes stored, code 1 and code 8. The LED always blinks the code number in one burst. For example a code 16 will make it blink sixteen times.

CEL comes on with a code 1 after driving a few miles means that the O2 sensor is bad, or unplugged.

 

Oh, ok, duh. I am used to the first flash(s) representing the 1st digit of the code, and the rapid flashes that follow being the 2nd digit of that code. I will check out my o2 sensor (code 1), and research this TDC Sensor, (code 8). Thank you very much. Happy Wrenching!