Test NTC-11: Checking Oxygen Sensor Heater

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION . For wiring diagram, see WIRING DIAGRAMS article.

NOTE: Upstream oxygen sensor may also be referred to as 1/1 O2 sensor. Downstream oxygen sensor may also be referred to as 1/2 O2 sensor.

Turn ignition on with engine off. Using scan tool, actuate oxygen sensor heater test. Oxygen sensor heater test may also be referred to as O2 sensor heater test. Wait 2 minutes for oxygen sensor voltage to stabilize.
Using scan tool, read upstream oxygen sensor voltage. If upstream oxygen sensor voltage is .4-.6 volt, go to next step. If upstream oxygen sensor voltage is not .4-.6 volt, go to step 6 .
If upstream oxygen sensor voltage stays at .4-.6 volt, there is a problem in the sensor circuit. Using scan tool, stop oxygen sensor heater test. Turn ignition off. Disconnect upstream oxygen sensor connector. Upstream oxygen sensor is located on exhaust pipe, just above the catalytic converter.
Using ohmmeter, check resistance between ground and terminal No. 1 (Black wire) on wiring harness side of upstream oxygen sensor connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open on Black wire to ground connection. Ground connection is located near top of driver's side strut tower, next to remote battery cable terminal on strut tower. Perform TEST VER-2A .
Turn ignition on with engine off. Using scan tool, actuate oxygen sensor heater test. Using voltmeter, check voltage at terminal No. 2 (Dark Green/Orange wire) on wiring harness side of upstream oxygen sensor connector. If voltage is more than 10 volts, replace upstream oxygen sensor. Perform TEST VER-2A . If voltage is 10 volts or less, repair open on Dark Green/Orange wire between Auto Shutdown (ASD) relay and upstream oxygen sensor. ASD relay is located in power distribution center at driver's side front corner of engine compartment, near air cleaner assembly. Perform TEST VER-2A .
Ensure ignition is on with engine off. Using scan tool, actuate oxygen sensor heater test. Wait 2 minutes for oxygen sensor voltage to stabilize.
Using scan tool, read downstream oxygen sensor voltage. If downstream oxygen sensor voltage is .4-.6 volt, go to next step. If downstream oxygen sensor voltage is not .4-.6 volt, use scan tool to stop oxygen sensor heater test. Test is complete.
If downstream oxygen sensor voltage stays at .4-.6 volt, there is a problem in the sensor circuit. Turn ignition off. Disconnect downstream oxygen sensor connector. Downstream oxygen sensor is located on exhaust pipe, behind catalytic converter.
Turn ignition on with engine off. Using scan tool, actuate oxygen sensor heater test. Using voltmeter, check voltage at terminal No. 4 (Orange/Dark Green wire) on wiring harness side of downstream oxygen sensor connector. If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, repair open on Orange/Dark Green wire between fuse No. 1 (10-amp) and downstream oxygen sensor. Auto Shutdown (ASD) relay provides voltage to fuse No. 1 and downstream oxygen sensor. Fuse No. 1 and ASD relay are located in power distribution center at driver's side front corner of engine compartment, near air cleaner assembly. Perform TEST VER-2A .
Using scan tool, stop oxygen sensor heater test. Turn ignition off. Using ohmmeter, check resistance between ground and terminal No. 6 (Black wire) on wiring harness side of downstream oxygen sensor connector. If resistance is less than 5 ohms, replace downstream oxygen sensor. Perform TEST VER-2A . If resistance is 5 ohms or more, repair open on Black wire to ground connection.Ground connection is located near top of driver's side strut tower, next to remote battery cable terminal on strut tower. Perform TEST VER-2A .