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NTC-11A: Checking Ho2S Heater

NOTE: 1/1 Heated Oxygen Sensor (HO2S) is located in upstream position. On models with 2 upstream HO2S, 1/1 HO2S is located in left upstream position. On AN body (2WD) with 5.9L engine and BE/BR bodies with 8.0L medium-duty engine, 1/2 Heated Oxygen Sensor (HO2S) is located in pre-catalyst position. On all other bodies, 1/2 HO2S is located in downstream position. On models equipped with 4 HO2S, 1/2 HO2S is located in left downstream position. 1/3 HO2S is used on BE/BR bodies with 8.0L medium-duty engine only and is located in post-catalyst position. 2/1 HO2S is located in right upstream position on models with 2 upstream HO2S.
  1. Turn ignition on, with engine off. Using scan tool, actuate HO2S heater test. Wait 2 minutes for HO2S voltages to stabilize. Using scan tool, read HO2S signal voltage. If voltage is one volt or less on all HO2S, stop actuation test. Test is complete. If voltage is more than one volt on any HO2S, stop actuation test and go to next step.
    NOTE: For circuit identification and wiring diagram, see appropriate wiring diagram in WIRING DIAGRAMS article.
  2. Turn ignition off. Disconnect suspected HO2S connector. Clean and/or repair connector as necessary. Using an ohmmeter, check resistance between ground and HO2S connector, heater ground circuit. If resistance is less than one ohm, go to next step. If resistance is one ohm or more, repair open heater ground circuit. Perform TEST VER-2A.
    NOTE: Voltage remaining above one volt on any HO2S, indicates a problem with that HO2S.
    NOTE: For circuit identification and wiring diagram, see appropriate wiring diagram in WIRING DIAGRAMS article.
  3. Turn ignition on, with engine off. Using scan tool, read HO2S signal voltage. If voltage is one volt or less on all HO2S, stop actuation test. Test is complete. If voltage is more than one volt on any HO2S, turn ignition off. Disconnect suspect HO2S connector. Clean and/or repair connector as necessary. Using a voltmeter, check voltage on HO2S connector, ASD relay output circuit. If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, repair open ASD relay output circuit. Perform TEST VER-2A.
  4. At this time, suspected HO2S is assumed to be defective. Replace HO2S. Perform TEST VER-2A.
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