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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 GOOD TRIP counter is displayed and equal to zero, go to step  3 . If GOOD TRIP counter is not displayed and equal to zero, go to next step.
  2. Turn ignition off. Wait at least 8 minutes to allow HO2S to cool until HO2S voltage has stabilized. Using scan tool, actuate O2 HEATER TEST. Using scan tool, monitor 2/1 HO2S voltage for at least 2 minutes. If voltage stays between .4 and .6 volt, go to next step. If voltage does not stay between .4 and .6 volt, go to step  7 .
  3. Turn ignition off. Allow HO2S to cool to room temperature. Disconnect 2/1 HO2S harness connector. Measure resistance between HO2S connector (component side) terminals No. 1 (Black wire) and No. 2 (Orange/Dark Green wire). If resistance is 4-7 ohms, go to next step. If resistance is not 4-7 ohms, replace HO2S.
  4. 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 between 2/1 HO2S harness connector and ground located behind left headlight.
  5. Turn ignition on. Using scan tool, actuate O2 HEATER TEST. Measure voltage between ground and ASD relay output circuit (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 ASD relay output circuit. See WIRING DIAGRAMS article.
  6. If no other possible causes are remaining, PCM is assumed to be defective. Replace PCM.
  7. Conditions that set DTC are not present at this time. Perform the following to help identify intermittent condition:
    • With engine running at normal operating temperature, wiggle wiring harness between 2/1 HO2S and PCM while monitoring 2/1 HO2S voltage on scan tool. If voltage changes or DTC sets while wiggling wiring harness, repair connectors or wiring harness where wiggling caused voltage to change or DTC to set.
    • Review freeze frame information on scan tool. Duplicate conditions present when DTC was set.
    • Refer to any technical service bulletins that may apply.
    • Visually inspect related wiring harness. Check for chafed, pierced, pinched or partially broken wires.
    • Visually inspect related wiring harness connectors. Check for broken, bent, pushed out or corroded terminals.

    If a problem is found, repair as necessary. If no problems are found, test is complete.

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