Heated Oxygen Sensors (HO2S) OPERATION TESTING ,REMOVAL and INSTALLATION?

OPERATION

See Figures 1 and 2

The oxygen sensor supplies the computer with a signal which indicates a rich or lean condition during engine operation. The input information assists the computer in determining the proper air/fuel ratio. A low voltage signal from the sensor indicates too much oxygen in the exhaust (lean condition) and, conversely, a high voltage signal indicates too little oxygen in the exhaust (rich condition).

Fig. Fig. 1: Typical Heated Oxygen Sensor (H2OS)-most vehicles are equipped with multiple sensors

The oxygen sensors are threaded into the exhaust manifold and/or exhaust pipes on all vehicles. Heated oxygen sensors are used on all models to allow the engine to reach the closed loop faster.

Fig. Fig. 2: Typical Heated Oxygen (HO2S) sensor mounting locations-Ranger shown, other models are similar

TESTING

WARNING

Do not pierce the wires when testing this sensor; this can lead to wiring harness damage. Back probe the connector to properly read the voltage of the HO2S.

1. Disconnect the HO2S.
2. Measure the resistance between PWR and GND terminals of the sensor. If the reading is approximately 6 ohms at 68°F (1°C). the sensor's heater element is in good condition.
3. With the HO2S connected and engine running, measure the voltage with a Digital Volt-Ohmmeter (DVOM) between terminals HO2S and SIG RTN(GND) of the oxygen sensor connector. If the voltage readings are swinging rapidly between 0.01-1.1 volts, the sensor is probably okay.

REMOVAL & INSTALLATION

See Figures 3 and 4

1996-99 Explorer/Mountaineers use four heated oxygen sensors (HO2S), and V6 equipped Rangers use three HO2S's, and 2.3L and 2.5L engines use two HO2S's for the engine control system. The heated sensors are located before and after the dual converters in the exhaust pipes. On 5.0L and 1991-95 engines V6 engines, there are two sensors, one is located in the left exhaust manifold and the other in the dual converter Y-pipe. 1991-95 2.3L engines use only one sensor.

1. Disconnect the negative battery cable.
2. Raise and safely support the vehicle on jackstands.

Fig. Fig. 3: From underneath, locate the oxygen sensor (arrow), which is screwed into an exhaust component

3. Disconnect the HO2S from the engine control sensor wiring.

If excessive force is needed to remove the sensors, lubricate the sensor with penetrating oil prior to removal.

Fig. Fig. 4: Using the proper wrench, loosen the oxygen sensor. Ensure that the wire and connector are unplugged

4. Remove the sensors with a sensor removal tool, such as Ford Tool T94P-9472-A.

To install:

5. Install the sensor in the mounting boss, then tighten it to 27-33 ft. lbs. (37-45 Nm).
6. Reattach the sensor electrical wiring connector to the engine wiring harness.
7. Lower the vehicle.
8. Connect the negative battery cable.

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