1990 Civic Check engine light comes on at high speeds--If shut the car off and restart it is fine until go over 70 mph--checked ecu get 2 messages one a single flash other 16 flashes?

The single flash indicates that there is no trouble code stored in the ECU. The 16 flashes indicate that the oxygen sensor is not functioning properly. This could be due to a faulty oxygen sensor, a problem with the wiring harness, or a vacuum leak.

Here are some things you can do to troubleshoot the problem:

- Inspect the oxygen sensor for damage. The sensor is located in the exhaust pipe, just before the catalytic converter. Look for any cracks or breaks in the sensor, as well as any signs of corrosion.

- Check the wiring harness for the oxygen sensor. Make sure that the wires are securely connected to the sensor and that there are no breaks or shorts in the harness.

- Check for vacuum leaks. A vacuum leak can cause the oxygen sensor to read incorrectly, which can lead to the Check Engine light coming on. Look for any loose or cracked hoses in the engine compartment.

If you are not able to find the problem, you may need to take your car to a mechanic for further diagnosis.