A2: Check O2 Sensor Heater Continuity

With EM021 disconnected, measure the resistance between EM021/001 & EM021/002.

Is the resistance between 4 & 10 ohms?

Yes
Go to A3 A3: Check For O2 Sensor Failure

No
Renew O2 sensor; reconnect plug(s)
Go to A6 A6: Stop