Sensing Something Awry Under the Hood Washington DC

By Gary Goms
3/26/2008

Once considered leading-edge technology, today's oxygen sensor has become a commonplace service item on modern vehicles.

O2 Sensor Diagnostics
Popularly introduced in the 1970s, the Lambda or, as it’s more popularly known, the oxygen sensor, rapidly became standard equipment as it’s a vital component of closed-loop or feedback fuel control technology. By using a voltage input from the oxygen sensor, a powertrain control module (PCM) can verify that its fuel control strategy is producing a chemically perfect 14.7:1 (by weight) air-to-fuel combustion ratio.

Operation Procedures
Before we venture into basic PCM operating strategies and diagnostic procedures, let’s review how a simple, single-wire zirconia oxygen sensor works in conjunction with the PCM. A closed-loop fuel control system must contain three essential components: an information processor (the PCM), an actuator (the fuel injector) and an exhaust gas sensor (the oxygen sensor).

During a cold startup, the PCM operates briefly in an open-loop or fixed fuel-control mode until the oxygen sensor reaches at least 600° F operating temperature. In the open-loop mode, the fuel injector pulse width is controlled by engine speed, load and temperature.

Photo 1

The fuel control system enters closed-loop operation when the oxygen sensor reaches 600° F operating temperature and begins generating a voltage signal to the PCM (See Phot...