To test the upstream O2 sensor on a 2011 Toyota Corolla, I backprobed it with a multimeter.
After I idled the engine for a few minutes to warm it up, the multimeter shows a steady voltage of 0.4V.
But I thought O2 sensors were supposed to fluctuate between 0.1 - 0.9V, so it looks like something is wrong.
After revving the engine to 2500rpm, the multimeter still shows a steady voltage of 0.4V.
What could this mean?