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DTC P0135: 1/1 O2 Sensor Heater Failure: Testing

NOTE: 1/1 HO2S may also be referred to as an upstream oxygen sensor. On 2.5L and 4.0L Federal models, 1/1 HO2S is located in exhaust downpipe in front of catalytic converter. On 4.0L Calif. models, 1/1 HO2S is located in front exhaust manifold.
  1. Turn ignition on. Using scan tool, check for DTCs. If GOOD TRIP counter is displayed for DTC P0135 and displayed count is "0", go to next step. If GOOD TRIP counter is not displayed for DTC P0135 or displayed count is not "0", go to step  3 .
  2. Turn ignition off and wait 8 minutes or more to allow HO2S to cool down. Turn ignition on. Using scan tool, actuate HO2S HEATER TEST and monitor 1/1 HO2S voltage for 2 minutes or more. If voltage stays at 0.4-0.6 volt, go to next step. If voltage does not stay at 0.4-0.6 volt, go to step  7 .
  3. Turn ignition off. Allow 1/1 HO2S to cool down to room temperature. Disconnect 1/1 HO2S connector. Measure resistance between Orange/Dark Green and Brown/Orange wires at 1/1 HO2S harness connector (component side). If resistance is not 4-5 ohms, replace 1/1 HO2S. If resistance is 4-5 ohms, 1/1 HO2S heater element is okay. Go to next step.
  4. Ensure ignition is off. Disconnect PCM connectors. PCM is located on firewall in right rear corner of engine compartment. Inspect connectors for damaged pins, corrosion and loose terminals. Repair connectors as necessary. If connectors are okay, measure resistance of Brown/Orange wire between 1/1 HO2S harness connector and terminal C8 at PCM C3 harness connector. See Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Brown/Orange wire.
  5. Ensure ignition is off. Reconnect PCM connectors. Turn ignition on. Ensure 1/1 HO2S is still disconnected. Using scan tool, actuate HO2S HEATER TEST. Measure voltage between ground and Orange/Dark Green wire at 1/1 HO2S harness connector. If voltage is more than 11 volts, go to next step. If voltage is 11 volts or less, repair open in power circuit to 1/1 HO2S heater. See WIRING DIAGRAMS article.
  6. At this time, PCM is assumed to be defective. Replace PCM.
  7. At this time, conditions for DTC to set do not exist or fault is an intermittent problem. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Using scan tool, monitor 1/1 HO2S voltage while wiggling connectors and wiring harness from 1/1 HO2S to Powertrain Control Module (PCM). PCM is located on firewall in right rear corner of engine compartment. If voltage changes while wiggling connectors and wiring harness, repair connectors and wiring harness where wiggling caused voltage to change. If voltage does not change, review FREEZE FRAME data using scan tool. Attempt to duplicate condition that caused DTC to set by paying special attention to the conditions during which 1/1 HO2S is monitored. Check for any related technical service bulletins that may apply. Visually inspect related connectors and wiring harness. Repair connectors and wiring harness as necessary. See WIRING DIAGRAMS article. If no problems are indicated, test is complete.
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