3. Check HO2S1 Ground Circuit For Open And Short

1. Disconnect heated oxygen sensor 1 harness connector.
2. Check harness continuity between HO2S1 terminal 4 and ground.

   Refer to Wiring Diagram.

   1. Continuity should exist. 
3. Also check harness for short to power.

OK or NG 

OK: GO TO 4.

NG: Repair open circuit or short to power in harness or connector.