DTC P1173 - Left Front Oxygen Sensor, Activity Not 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 left front oxygen sensor signal voltage exceeds .55 volt and remains unchanged for 42 seconds after engine is started and has reached normal operating temperature. Engine speed at 1150 RPM or greater. Possible causes are:

Left front heated oxygen sensor.
Open or short circuit between terminal No. 3M on Engine Control Module (ECM) and terminal "A" (Yellow wire) on left front oxygen sensor.
Intake air system, fuel system and/or ignition system malfunction.