I am working on a 2004 civic dx with the d17A1 engine. The car was giving me 2 codes, 2770 and 135. 2770 was an easy wire fix; but I can't locate the problem to fix 135(heater circuit malfunction primary o2 sensor).I have replaced the ground wire from the sensor to the ecu because there was a short in it and I have tried a Bosch and a Denso sensor thinking this was the problem but I still get code 135. I have a manual from ALLDATAdiy.com :: Leading Source of Diagnostic and Repair Information and have followed the troubleshooting flow chart and everything checks out good. The ecu controls the ground circuit and that is why I think the ecu needs replaced, what about you?