4A Fault Code 21 Oxygen Sensor Circuit

1. Connect diagnostic read-out tool to engine test connector, then turn the ignition switch Off.
2. Disconnect oxygen sensor electrical connector.
3. Connect a jumper wire to oxygen sensor electrical connector.
4. Start engine.
5. Contact other end of jumper wire to battery positive and ground terminals and note read-out tool display. Divide diagnostic read-out tool reading by 10.
6. If display on read-out tool indicates voltage when jumper wire is connected to battery positive terminal and indicates no voltage when jumper wire is connected to battery ground terminal, replace oxygen sensor.
NOTE: Before replacing the oxygen sensor make sure the jumper wire between it and the engine harness is not open.
7. If display read-out tool does not indicate voltage when jumper wire is connected to battery positive terminal, proceed to Test 4 step B.