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Home >> Subaru >> 2001 >> Outback Base, Automatic >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> Engine Controls - Self-Diagnostics - 2.2L & 2.5L >> Diagnostic Tests >> DTC P0141: Rear Ho2S Heater Circuit Malfunction/Low Input - Forester & IMPREZA 2.5L

DTC P0141: Rear Ho2S Heater Circuit Malfunction/Low Input - Forester & IMPREZA 2.5L

  1. Perform basic diagnostic procedure. See BASIC DIAGNOSTIC PROCEDURE . Turn ignition off. Disconnect ECM connector B134 (35-pin connector). Using an ohmmeter, measure resistance between ECM connector B134 (35-pin connector) terminals No. 34 and No. 35 and ground. See Figure. If resistance is less than 5 ohms, go to next step. If resistance is not less than 5 ohms, locate and repair open circuit in wiring and check for poor terminal contact in connectors between ECM and rear HO2S.
  2. Reconnect all disconnected connectors and start engine. Observe rear HO2S heater current on scan tool. If current draw is more than 0.2 amp, repair poor terminal contact in connectors between ECM and rear HO2S sensor. If current draw is not more than 0.2 amp, go to next step.
  3. With engine idling, use a DVOM connected to ground and backprobe ECM connector B134 (35-pin connector) terminal No. 21. If voltage is less than one volt, go to step  6. If voltage is not less than one volt, go to next step.
  4. Start and idle engine. Using a DVOM connected to ground, backprobe ECM connector B134 (35-pin connector) terminal No. 21 while wiggling harness and ECM connector. If voltage changes less than one volt while wiggling harness and ECM connector, check for poor terminal contact at ECM connector. If voltage does not change less than one volt while wiggling harness and ECM connector, go to next step.
  5. Turn ignition off. Disconnect rear HO2S electrical connector. Turn ignition on. With DVOM connected to ground, backprobe ECM connector B134 (35-pin connector) terminal No. 21. If voltage is less than one volt, replace ECM. If voltage is not less than one volt, locate and repair short to voltage in wiring between ECM and rear HO2S. After repair, replace ECM.
  6. Turn ignition off. Remove main relay. Connect battery voltage to main relay terminals No. 1 and No. 2. Using an ohmmeter, measure resistance between main relay terminals No. 4 and No. 6. If resistance is less than 10 ohms, go to next step. If resistance is not less than 10 ohms, replace main relay.
  7. Turn ignition off. Disconnect rear HO2S harness connector. Turn ignition on. Using a DVOM connected to ground, measure voltage at rear HO2S harness connector terminal No. 2. See Figure. If voltage is more than 10 volts, go to next step. If voltage is not more than 10 volts, locate and repair open circuit in wiring and check for poor terminal contact in connectors between main relay and rear HO2S.
  8. Turn ignition off. Using an ohmmeter, measure resistance between rear HO2S connector terminals No. 1 and No. 2. If resistance is less than 30 ohms, locate and repair open circuit in wiring between rear HO2S and ECM. If resistance is not less than 30 ohms, replace rear HO2S. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
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