Help

Maybe others have had this problem: 96 Civic EX. Check engine light goes on. Car has 98,000 mi on it. I figured it had to be the O2 sensor. I replaced the 02 sensor in about 5 min, started it back up, the CEL was off, drove it home. The next morning the CEL was back on. I hooked up the scanner and it's throwing up a P0135 code, which is a o2 sensor heater circuit malfunction. So thinking that it might be a faulty O2 sensor, I replaced it with a new one, and the CEL was still on. I got a wiring digram, located the wires for the O2 sensor heater. I tested them on the engine side of the O2 sensor, and was getting a signal. Tested them at the ECU and got a signal. Finally, I tested them at the junction relay on the drivers side of the engine compartment, and got a signal there too. The CEL is still on and I am out of things to check. If anyone knows anything please let me know.