I recently got a MIL light on, on my wife's Aveo 1.5LS and I used my scan tool and got a P0131 & P0134 error. I cleared the codes and drove around the block and the MIL light came back on. Scanned and got the same two error codes. I measured voltage on the connector that goes to the ECU and got 0.4V. I measure no resistance on the O2 sensor side. I don't know if I do the measurements correctly. I just measure straight on the two wires. Some websites suggest measure between the sense on the connector and ground on the block. Any advice? I want to replace the O2, but it's bit expensive so I want to be 100% sure it's the O2. Thank you.