DTC P0140 HEATED OXYGEN SENSOR 2 (REAR) (PLAUSIBILITY); Component Description; CONSULT-II Reference Value; ECM Terminals and Reference Value; On Board Diagnosis Logic
EF & EC-7139spec tableSource page-title/DTC-code mismatch preserved: page title says "DTC P0140 ... (PLAUSIBILITY)" but the DTC code in the on-board-diagnosis table is "P0138". Standard OBD ordering is P0138 HIGH VOLTAGE / P0140 NO ACTIVITY — this Nissan service manual conflates the two. Source typos preserved: "mordenately" (inordinately), "grond".
CG10, CGA3
Component Description
The heated oxygen sensor 2 (rear), after three way catalyst, monitors the oxygen level in the exhaust gas.
Even if switching characteristics of the heated oxygen sensor 1 (front) are shifted, the air fuel ratio is controlled to stoichiometric, by the signal from the heated oxygen sensor 2 (rear).
This sensor is made of ceramic zirconia. The zirconia generates voltage from approximately 1V in richer conditions to 0V in leaner conditions.
CONSULT-II Reference Value in Data Monitor Mode
Specification data are reference values.
CONSULT-II Data Monitor — HO2S2
HO2S2 (B1)
CONDITIONEngine: After warming up — Revving engine from idle to 3,000 rpm
SPECIFICATION0 - 0.3V ↔ Approx. 0.6 - 1.0V
HO2S2 MNTR (B1)
CONDITIONEngine: After warming up — Revving engine from idle to 3,000 rpm
SPECIFICATIONLEAN ↔ RICH
ECM Terminals and Reference Value
Specification data are reference values and are measured between each terminal and ground.
CAUTION
Do not use ECM ground terminals when measuring input/output voltage. Doing so may result in damage to the ECM's transistor. Use a grond other than ECM terminals, such as the ground.
ECM Terminals — Heated Oxygen Sensor 2 (Rear)
39
Wire colorW/R
ItemHeated oxygen sensor 2 (rear)
Condition[Engine is running]
- After warming up to normal operating temperature and engine speed is 2,000 rpm
Data (DC Voltage)0 - Approximately 1.0V
On Board Diagnosis Logic
The heated oxygen sensor 2 (rear) has a much longer switching time between rich and lean than the heated oxygen sensor 1 (front). The oxygen storage capacity before the three way catalyst causes the longer switching time. To judge the malfunctions of heated oxygen sensor 2 (rear), ECM monitors whether the output voltage is mordenately high during various driving conditions such as fuel-cut.