E4: Check For O2 Sensor Failure

With the conditions held as E3, suddenly decelerate to idle.

Has the voltage dropped to 400mV or less?

Yes
GO to E5, E5: Check For O2 Sensor Failure

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