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DTC P0155: 2/1 O2 Sensor Heater Failure: Testing

NOTE: 2/1 HO2S may also be referred to as an upstream oxygen sensor. 2/1 HO2S is located in outlet flange of left exhaust manifold.
  1. Turn ignition on. Using scan tool, read DTCs. If GLOBAL GOOD TRIP counter is displayed and displayed count is "0", go to next step. If GLOBAL GOOD TRIP counter is not displayed or displayed count is not "0", go to step  6.
  2. Turn ignition off. Disconnect 2/1 HO2S connector. Turn ignition on. Using scan tool, actuate HO2S HEATER TEST. Using a voltmeter, measure voltage between ground and Orange/Dark Green wire at 2/1 HO2S harness connector. If voltage is more than 11 volts, go to next step. If voltage is 11 volts or less, repair open in HO2S heater voltage input circuit (Orange/Dark Green wire) between power distribution center and 2/1 HO2S. See WIRING DIAGRAMS article.
  3. Turn ignition off. Using ohmmeter, measure resistance between ground and Black wire at 2/1 HO2S harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in heater ground circuit (Black wire). See WIRING DIAGRAMS article.
  4. Measure resistance between Orange/Dark Green wire and Black wire at 2/1 HO2S connector (component side). If resistance is 3-7 ohms, go to next step. It resistance is not 3-7 ohms, replace 2/1 HO2S.
  5. At this time, PCM is assumed to be defective. Replace PCM.
  6. Turn ignition off. Visually inspect related connectors and wiring harness for damage. Repair connectors and wiring harness as necessary. If connectors and wiring harness are okay, reconnect all connectors. Start engine. Wiggle 2/1 HO2S connector and wiring harness while monitoring scan tool display. If GOOD TRIP counter display count changes to "0", repair connector or wiring harness where wiggling caused display to change. If GOOD TRIP counter display count does not change to "0", no problem is indicated at this time. Check for any related technical service bulletins that may apply.
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