Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1995 Subaru Legacy BaseFACTORY OEM SERVICE PROCEDURE
DTC P0141 (RO2_H) - Rear Oxygen Sensor (O2S) Heater Circuit Malfunction
- Turn ignition to OFF. After Connecting SSM or OBD-II scan tool, turn ignition to ON. Turn SSM or OBD-II scan tool to ON. Start engine. on SSM, select function mode F30 to read rear O2S heater current indication. If reading is less than 0.2 amp, go to step 2). If reading is 0.2 amp or more, repair poor contact in rear O2S connector or ECM connector.
- Start and idle engine. Measure voltage between ECM connector B84, terminal No. 43 and ground. If voltage is 1.0 volt or less, go to next step. If voltage is less than 1.0 volt while shaking harness and connector of ECM, repair poor contact in ECM connector. If voltage remains 1.0 volt or less, go to next step. Disconnect rear O2S connector. Measure voltage between ECM connector B84, terminal NO, 43 and ground. If voltage is 1.0 volt or less, replace ECM. If voltage is more than 1.0 volt, repair short in harness between ECM and rear O2S connector. After repair of short in harness, replace ECM.
- Turn ignition to OFF. Disconnect rear O2S connector. Turn ignition to ON. Measure voltage between rear O2S connector T6, terminal No. 2 and ground. If voltage is 10 volts or more, go to step 4). If voltage is less than 10 volts, repair poor contact in connector or open circuit in harness between main relay and rear O2S.
- Turn ignition to OFF. Measure resistance between rear O2S connector T6, terminals No. 1 and 2. If resistance is more than 30 ohms, replace rear O2S. If resistance is 30 ohms or less, repair open circuit between rear O2S connector and ECM connector, poor contact in rear O2S connector, poor contact in ECM connector or poor contact in rear O2S connecting harness connector.
Factory Service Tools
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.