just had two O2 sensors die... electrical problem?
 

My car sat for 6mo, and afterwards I had two oxygen sensors die, right away. The first was an OEM type, and it worked for a day, then started reading 0v (according to megasquirt). Then I popped in a spare 4-wire bosch, and it was also reading 0v. I checked it with a multimeter, and it's actually reading between -0.75v and 0.050v. So, the range appears to have gone negative.

I'm not really sure what the culprit is, so I'm trying to figure out whether it's an electrical or mechanical problem.

I disconnected the O2 sensor harness, and checked the voltage of the line going into the ecu, and surprisingly it's reading 0.025v -- that's without the sensor connected. So it looks like I'm getting a small amount of voltage going back to the sensor.

I checked the voltage from the blue 12v terminal and the engine, and am getting 14.42v. Between 12v and the chassis ground I'm getting 14.40v. So there is a small difference between the grounds (0.02v).

Any tips on how to further troubleshoot this? I'm just learning how to diagnosis electrical systems on cars, so I'm not really sure if the values above are normal or not!

Thanks,
Justin

Edit: I cleaned off the ground strap as well as one of the chassis grounds, and now the difference between the grounds is less than 0.01v. However, I'm still getting the same 0.025v reading on the O2 sensor line going into the ECU (with no O2 sensor attached).

Edit2: Also, I plugged in my megasquirt, and now the O2 sensor line only has 0.05v on it. Not sure what that means though....