DTC P0140 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2): Wiring Diagram

WARNING: This page is about a different variant/trim than selected.

Fig 1: HO2S Heater Control Low (Bank 1 Sensor 2) - Wiring Diagram

G06647758

Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC PROCEDURE

Step	Check	Yes	No
1 CHECK REAR OXYGEN SENSOR DATA . Warm up the engine until engine coolant temperature is above 75°C (167°F), and keep the engine speed at 3,000 RPM. (2 minutes maximum) Read the data of rear oxygen sensor signal using Subaru Select Monitor or general scan tool. NOTE: Subaru Select Monitor For detailed operation procedures, refer to "READ CURRENT DATA FOR ENGINE". Ref. to SUBARU SELECT MONITOR . General scan tool For detailed operation procedures, refer to the general scan tool operation manual.	Is the voltage 490 mV or more?	Go to step 6 .	Go to step 2 .
2 CHECK REAR OXYGEN SENSOR DATA . Warm up the engine until engine coolant temperature is above 75°C (167°F), and rapidly reduce the engine speed from 3,000 RPM. Read the data of rear oxygen sensor signal using Subaru Select Monitor or general scan tool. NOTE: Subaru Select Monitor For detailed operation procedures, refer to "READ CURRENT DATA FOR ENGINE". Ref. to SUBARU SELECT MONITOR . General scan tool For detailed operation procedures, refer to the general scan tool operation manual.	Is the voltage 250 mV or less?	Go to step 6 .	Go to step 3 .
3 CHECK REAR OXYGEN SENSOR CONNECTOR AND COUPLING CONNECTOR .	Has water entered the connector?	Completely remove any water inside.	Go to step 4 .
4 CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR . Turn the ignition switch to OFF. Disconnect the connector from ECM and rear oxygen sensor. Measure the resistance of harness between ECM and rear oxygen sensor connector. Connector & terminal (B136) No. 20 - (E25) No. 3: (B135) No. 30 - (E25) No. 4:	Is the resistance less than 1 Ω?	Go to step 5 .	Repair the harness and connector. NOTE: In this case, repair the following item: Open circuit in harness between ECM and rear oxygen sensor connector Poor contact of coupling connector
5 CHECK HARNESS BETWEEN ECM AND REAR OXYGEN SENSOR CONNECTOR . Connect the connector to ECM. Turn the ignition switch to ON. Measure the voltage between rear oxygen sensor connector and chassis ground. Connector & terminal (E25) No. 3 (+) - Chassis ground (-):	Is the voltage 0.2 - 0.5 V?	Replace the rear oxygen sensor. Ref. to REAR OXYGEN SENSOR .	Repair the harness and connector. NOTE: In this case, repair the following item: Open circuit in harness between ECM and rear oxygen sensor connector Poor contact of ECM connector Poor contact of coupling connector
6 CHECK EXHAUST SYSTEM . Check exhaust system parts. NOTE: Check the following items. Looseness and improper fitting of exhaust system parts Damage (crack, hole etc.) of parts Damage (crack, hole etc.) between front oxygen (A/F) sensor and rear oxygen sensor	Is there any fault in exhaust system?	Repair or replace faulty parts.	Replace the rear oxygen sensor. Ref. to REAR OXYGEN SENSOR .