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DTC P0141 (RO2_H): Rear O2S Heater Circuit Malfunction

  1. Connect scan tool and check for DTC(s). If DTC P0141 is only code set, go to step 3). If DTC P0135 also exists, go to next step.
  2. Turn ignition off. Disconnect PCM connector. Using an ohmmeter, check resistance of harness between ground and PCM connector terminal No. 42 (Black/White wire on Forester and Legacy, or Black/Yellow wire on Impreza). If resistance is 5 ohms or less, repair poor contact in PCM connector. If resistance is more than 5 ohms, check for an open in harness or poor contact in rear O2S connector.
  3. Start engine. Observe rear O2S heater current display. If reading is 0.2 amp or less, go to next step. If reading is more than 0.2 amp, check for poor contact at PCM and rear O2S connectors.
  4. Using voltmeter connected to ground, backprobe PCM connector terminal No. 37 (Brown/White wire on Forester and Legacy, or White/Blue wire on Impreza). If voltage is one volt or less, go to step 6). If voltage is more than one volt, wiggle PCM wiring and connector. If voltage changes to one volt or less, repair poor contact in PCM connector. If voltage remains one volt or more, leave voltmeter connected and go to next step.
  5. Disconnect rear O2S connector. Using a voltmeter connected to ground, backprobe PCM connector terminal No. 37 (Brown/White wire on Forester and Impreza, or White/Blue wire or Legacy). If voltage is one volt or less, replace PCM. If voltage is more than one volt, check for short in wiring between PCM and rear O2S connector. Repair circuit as necessary. After repairing short, check PCM operation and replace if necessary.
  6. Turn ignition off. Disconnect rear O2S connector. Turn ignition on. Using a voltmeter connected to ground, measure voltage at rear O2S connector terminal No. 2 (Yellow/Red wire). If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, check for poor contact in connectors or open circuit in wiring between main relay and rear O2S.
  7. Turn ignition off. Check resistance of rear O2S between connector terminals No. 1 (White/Blue wire) and No. 2 (Yellow/Red wire). If resistance is more than 30 ohms, replace rear O2S. If resistance is 30 ohms or less, check for an open in wiring between rear O2S and PCM connector and/or poor contact in rear O2S or PCM connectors.
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