Code 65 says 2ndary O2 sensor heater in my '98/'99 Accord Helm book, so I think it's good.

The 2ndary O2 sensor doesn't control anything, it just tells the ECU whether the cat is working or not. And it's heater simply gets that O2 sensor working sooner when you start the car.

Unplug that sensor, it's under the car right after the cat. Find the 2 same-color (black?) wires on the sensor. The resistance between them should be 15 to 40 ohms, with no continuity to ground from either one. If that's no good, get a new sensor.

If that's good, then you can start looking for broken wiring on the circuit that connects to those 2 terminals.