2007 Honda Wagovan O2 sensor

You have to connect a scanner to view live data, then watch the signal voltage. For the sensors before the catalytic converter, the voltage should switch from below about 0.5 volts to above 0.5 volts roughly twice per second. For sensors after the catalytic converter, the voltage should change very slowly, as in maybe once or twice every couple of minutes.

The Engine Computer tests the oxygen sensors for you. If there are no stored diagnostic fault codes and the Check Engine light is not on, there's no need to suspect a problem with the O2 sensors.