4A Fault Code 21 Oxygen Sensor Circuit

*** UPDATED BY TSB #18-61-86

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 3 way electrical connector with black wire.
4. Put the system into sensor test mode 02.
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. When the jumper wire is on the positive post, the display on the readout box increases towards 5 volts or when the jumper wire is on the negative post the display on the readout box decreases towards 0 volts, replace the oxygen sensor.
7. If display read-out tool does not indicate 5 volts when jumper wire is connected to battery positive terminal, proceed to step B. 4B Oxygen Sensor Circuit