Suzuki Forum - Suzuki Enthusiast Forums - O2-sensor and ECM question

Hi, my 2003 xl-7 with only 30k miles got the P0135 fault code. The repairshop told me the sensor had to be replaced so naturally I took upon myself to do just that. I still get the P0135 fault code. The battery neg. was detached during the repair. Heater relay is working. So I would like to know:
Is it safe to make a continuity check on the gray cable from the relay socket to the ECM. As both heater relays are fed from the same source and each relay coil is sunk over individual transistors in the ECM, can I just go about and measure continuity in the offending cable without risking anything bad happening to the ECM? Should this be done with battery disconnected and harness connector pulled from the ECM? Engine=H27a

Any help appreciated!