See Figures 1, 2 and 3
The Oxygen Sensor (O 2 S) reacts to the oxygen in the exhaust gases and sends a voltage to the Engine Control Module (ECM) based on the reaction. A low voltage indicates too much oxygen in the exhaust or a lean conditions. A high voltage indicates not enough oxygen in the exhaust or a rich condition. The ECM uses this information to vary the air/fuel mixture. The oxygen sensor is located in the exhaust stream, ahead of the catalytic converter.
Most Ford vehicles use a heated oxygen sensor. The heated element keeps the sensor at proper operating temperature during all operating modes. Maintaining correct sensor temperature at all times allows the system to enter closed loop operation sooner and to remain in closed loop operation during periods of extended idle.
- Disconnect the O 2 S. Measure resistance between the sensor connector terminals PWR and GND (heater). If the reading is 2-30 ohms, the sensor's heating element is okay.
- With the O 2 S connected and the engine running at normal operating temperature, measure voltage with DVOM between sensor connector terminals HO 2 S and SIG RTN . If the voltage reading is 0-1.0V at idle and 0.5-1.0V when accelerating, the sensor is okay.