1990 Civic, 5-sp 240k miles.

We had a code 1 dtc, found by counting the flashes on the ecu window when turning the key on. We replaced the o2 sensor with a new bosch sensor.

Had the battery unhooked to reset the code, and the car ran and drove fine for about 20 minutes then the CEL came back on. Any suggestions? The wire's all seem fine.
TIA

 

Here is the troubleshooting to make sure the wiring is alright. Hopefully this will help you out.

 

Thank you! I'll give this a try.