Thought we'd be clever and unplug the downstream O2 sensor and maybe find out that was the real problem with the voltage spike. First I cleared the P0134 upstream O2 sensor code and dash check engine light. I got under and unplugged the downstream O2 sensor at the connection. Start the engine and expected to see the check engine light but nothing yet so I drive the van and as usual in about the same driving distance/time the check engine light appears. Do the 3x key on off cycle and the P0134 code and only that code appears at the odometer and nothing for the downstream (which I don't at this point know what that would be?). I was hoping to see only the downstream or a new/different code or at the worst both the P0134 and a new code for the downstream O2 sensors but still only one code P0134. It doesn't recognize that I've unplugged the downstream O2 sensor I plugged in my "pocket" INNOVA scanner/code reader and the same results just P0134. What do you guys think, is it ECM time??