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DTC P0037: Rear Ho2S Heater Circuit Malfunction - Legacy & Outback 2.5L A/T

  1. Perform basic diagnostic procedure. See BASIC DIAGNOSTIC PROCEDURE . Turn ignition off. Disconnect ECM connector B134 (35-pin connector). Using an ohmmeter connected to ground, measure resistance at ECM connector B134 (35-pin connector) terminal No. 35. See Figure. If resistance is less than 5 ohms, go to step  3. If resistance is not less than 5 ohms, go to next step.
  2. Using an ohmmeter connected to ground, measure resistance at ECM connector B134 (35-pin connector) terminal No. 34. If resistance is less than 5 ohms, go to step  3. If resistance is not less than 5 ohms at either terminal No. 34 or No. 35, locate and repair open circuit in wiring and check for poor terminal contact in connectors between ECM and ground point.
  3. Start engine. Using scan tool, observe rear HO2S heater current value. If current draw is not more than 0.2 amp, go to next step. If current draw is more than 0.2 amp, check for poor terminal contact in connectors between ECM and rear oxygen sensor.
  4. Start and idle engine. Using a DVOM connected to ground, measure voltage at ECM connector B134 (35-pin connector) terminal No. 21. If voltage is less than one volt, go to step  7. If voltage is not less than one volt, go to next step.
  5. Measure voltage between ECM connector B134 (35-pin connector) terminal No. 21 and ground while wiggling harness and ECM connector. If voltage changes less than one volt while wiggling harness and connector, repair poor terminal contact in connectors. If voltage does not change less than one volt while wiggling harness and connector, go to next step.
  6. Turn ignition off. Disconnect electrical connector from rear oxygen sensor. Turn ignition on. Using a DVOM connected to ground, measure voltage at 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 circuit in wiring between ECM and rear oxygen sensor. After repair, replace ECM.
  7. With electrical connector disconnected from rear oxygen sensor, measure voltage between rear HO2S connector terminal No. 2 and ground. See Fig 1. 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 oxygen sensor.
  8. Turn ignition off. Measure resistance across rear oxygen sensor connector terminals No. 1 and No. 2. If resistance is less than 30 ohms, locate and repair open circuit in wiring and check for poor terminal contact in connectors between ECM and rear oxygen sensor. If resistance is not less than 30 ohms, replace rear oxygen sensor. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
Fig 1: Rear HO2S Connector Terminal Identification
G00013011Courtesy of SUBARU OF AMERICA, INC.
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