DR-5A Fault Code 21 Oxygen Sensor Circuit

1. With diagnostic read-out tool connected to engine test connector, turn ignition switch Off, then disconnect oxygen sensor connector.
2. Connect a jumper wire to oxygen sensor electrical connector.
3. Place system in Sensor Test Mode 02. Note that display readings must be divided by 10.
4. Touch other end of jumper wire to positive post of battery, then to negative battery post.
5. If display read-out increases towards 5 volts when touching positive post or decreases toward 0 volts when touching negative post, replace oxygen sensor.
6. If display read-out does not increase or decrease, proceed to Test 5 step B.