B4: Check For O2 Sensor Failure

Run the engine for a period to warm the sensor & then maintain a steady speed of approximately 2500 rpm Measure the voltage between EM021/003 & EM021/004.

Is the voltage between 600mV & 1.0 Volt?

Yes
Go to B5

No
Renew O2 sensor, reconnect plug(s)
Go to B8