DTC P0140 - Right Rear Heated Oxygen Sensor, Insufficient Activity Detected: Condition

WARNING: This page is about a different car, the 1997 Mazda Millenia. However, it is still accessible from the selected car via links, so may be relevant.

DTC is set when right rear heated oxygen sensor signal voltage does not exceed .55 volt after engine is started, or stays below .55 volt for 80 seconds after engine has reached normal operating temperature. Engine speed at 1150 RPM or greater. Possible causes are:

Right rear oxygen sensor.
Open or short circuit between terminal No. 3D on Engine Control Module (ECM) and terminal "A" (White wire) on right rear oxygen sensor.
Open circuit between terminal No. 3AB on Engine Control Module (ECM) and terminal "B" (Black/Yellow wire) on right rear oxygen sensor.
Intake air system, fuel system and/or ignition system malfunction.