My 1990 honda civic with 306000 miles runs good most of the time. Sometimes while I am driving it the car will just qiut and the check engine light will come on. I looked under the carpet on the passenger side and saw a red light blink 15&16 times. What is going on? Sometimes it will start right back up and sometimes it won't. Sometimes when it does start right back up it doesn't run very long till it quits again. Barry

Congratulations on going 306,000 miles in your Civic! Nice job.

15 blinks is Diagnostic Trouble Code (DTC) 15, Ignition Output Signal. Best bet is that your Ignition Control Module (igniter) inside your distributor is failing. It's pretty easy to replace. I would replace the coil at the same time, due to the mileage on the vehicle. If you do the work yourself, remove the coil first for easier access to the igniter. Remember to apply the enclosed silicone grease on the back of the igniter, before you mount it to the heat sink. It promotes heat transfer. Similarly, lightly coat the 4 male connectors on the igniter with silicone grease.

Here's what igniters look like and cost:

http://www.partsamerica.com/ProductList.aspx?PartType=194&PTSet=A&SearchFor=Ignition%20Module%2FControl%20Unit

16 blinks is DTC 16, Fuel Injector.

Disconnect the negative battery terminal for 15 seconds to reset your computer. Then, start and drive your car to verify which DTC it really is. It's probably DTC 15, based on your description of the symptoms.

Could it not be the notorious main relay? Just asking.