Test NTC-12: 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 upstream oxygen sensor circuit. Turn ignition off. Disconnect upstream oxygen sensor connector. Upstream oxygen sensor is mounted on exhaust manifold.
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, go to next step. 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 battery. Perform TEST VER-2A .
Using scan tool, stop oxygen sensor heater test. Turn ignition off. 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, replace upstream oxygen sensor. Perform TEST VER-2A . If resistance is 5 ohms or more, repair open on Black wire between upstream oxygen sensor and ground connection. Ground connection is located near rear of cylinder head or cylinder block. Perform TEST VER-2A .
Turn ignition off. Turn ignition 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 downstream oxygen sensor circuit. Turn ignition off. Disconnect downstream oxygen sensor connector. On 2.4L, downstream oxygen sensor is mounted near rear of catalytic converter. On 3.0L, 3.3L and 3.8L, downstream oxygen sensor is mounted on exhaust pipe, behind catalytic converter.
On all models, 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 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 Dark Green/Orange wire between Auto Shutdown (ASD) relay and downstream oxygen sensor. ASD relay is located in power distribution center at driver's side front corner of engine compartment, near battery. Perform TEST VER-2A .
Using scan tool, stop oxygen sensor heater test. Turn ignition off. Using ohmmeter, check resistance between ground and terminal No. 1 (Black/Tan wire on 3.0L early build, or Black wire on 2.4L, 3.0L late build, 3.3L and 3.8L) 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/Tan wire on 3.0L early build, or Black wire on 2.4L, 3.0L late build, 3.3L and 3.8L between downstream oxygen sensor and ground connection. Ground connection is located near rear of cylinder head or cylinder block. Perform TEST VER-2A .