E3: Check For O2 Sensor Failure

Run the engine for a period to warm the sensor and then maintain a steady speed of approximately 2500 rpm.
With EM023 disconnected, measure the voltage between EM023/003 and EM023/004.

Is the voltage between 600mV and 1.0 Volt?

Yes
GO to E4, E4: Check For O2 Sensor Failure

No
Renew O2 sensor. Reconnect plug(s)
GO to E7, E7: Heated O2 Sensor Short Circuit To Ground