DTC P0136: Rear Heated Oxygen Sensor (Ho2S) Circuit Malfunction (Forester, IMPREZA & Outback Sport)

Perform test procedure. See TESTING PROCEDURE . If DTC P0131 and/or P0132 are present, go to next step. If only DTC P0136 is present, go to step 3.
Perform diagnostic routine for DTC P0131 and/or P0132. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If cause of DTC P0131 and/or P0132 is not due to failure in fuel system, go to next step. If cause of DTC P0131 and/or P0132 is due to failure in fuel system, repair fuel system as necessary. Further inspection of DTC P0136 is not necessary. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES and VERIFICATION PROCEDURE .
Start and warm engine to more than 158°F (70°C). Operate engine at 2000-3000 RPM for 2 minutes. Using a scan tool, monitor rear heated oxygen sensor (HO2S) signal. If indicated value fluctuates, go to step 8. If indicated value does not fluctuate, go to next step.
Increase engine speed to 4500 RPM and hold for 5 seconds, quickly depress accelerator pedal fully, and then idle engine for 10 seconds. Repeat this procedure 3 times, then use a scan tool to monitor rear HO2S signal. If indicated value is fixed between 0.2-0.4 volt, go to next step. If indicated value is not fixed between 0.2-0.4 volt, replace rear HO2S. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES and VERIFICATION PROCEDURE .
Turn ignition off. Disconnect 30-pin ECM electrical harness connector B136 and 4-pin rear HO2S electrical harness connector. Using a DVOM, measure resistance between 30-pin ECM electrical harness connector B136 terminal No. 16 (Red/Green wire) and rear HO2S 4-pin electrical harness connector terminal No. 3 (Yellow/White wire). See Figure and Figure . If resistance is not more than 3 ohms, go to next step. If resistance is more than 3 ohms, locate and repair open circuit in wiring between ECM and rear HO2S. See ENGINE PERFORMANCE in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES and VERIFICATION PROCEDURE .
Turn ignition off. With 30-pin ECM electrical harness connector B136 disconnected, use a DVOM to measure resistance of Black/Red wires between 30-pin ECM electrical harness connector B136 terminals No. 21 and 22 and good engine ground point. If resistance is less than 5 ohms on both circuits, go to next step. If resistance is not less than 5 ohms on both circuits, repair open circuit in identified circuit between ECM and ground point located at center rear of engine. Also check contact of all connectors between ECM and ground point. See ENGINE PERFORMANCE in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES and VERIFICATION PROCEDURE .
Turn ignition off. Reconnect 30-pin ECM electrical harness connector B136 and leave 4-pin rear HO2S electrical harness connector disconnected. Turn ignition on. Using a DVOM, measure voltage of White wire between 4-pin rear HO2S electrical harness connector terminal No. 4 and good engine ground point. If voltage is more than 0.2 volt, replace rear HO2S. If voltage is not more than 0.2 volt, repair open circuit between rear HO2S and ECM. Also check for poor contact in all connectors between ECM and rear HO2S. See ENGINE PERFORMANCE in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES and VERIFICATION PROCEDURE .
Check for poor or loose HO2S installation, exhaust system leaks, holes and loose components between front oxygen sensor (A/F) and rear HO2S. Repair as needed. If no problems were found, replace rear HO2S. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES and VERIFICATION PROCEDURE .